Ion beam processing for thin film deposition is rapidly overtaking some of the more conventional plasma-based thin film processing techniques. This is due to strong improvements in the types and reliabilities of the sources available as well as a growing understanding of the advantages and capabilities of using ion beams.

An ion beam process can be differentiated from a plasma-based process in that the plasma in an ion beam is generated away from the sample and a beam of ions is directed at the sample. In a plasma-based process, the sample is usually immersed in the plasma. This highlights the fundamental advantage of ion beam processing—control of the flux and energy of the ions incident on either a sample or a target (for sputter deposition). It is this control which is missing in plasma-based processing, where the ion flux (current), ion energy, chamber pressure, and gas species are all hopelessly intertwined. In addition, certain aspects of the ion bombardment—angle of incidence, complications of gas scattering, etc. —are essentially fixed in plasma-based processing, leaving no room to vary parameters, and in conjunction, film properties.

A wealth of different types of ion sources cover a broad range of beam currents and energies. At the high energy end (0.1 – 20 MeV) are the implantation sources, typically used for doping semiconductors and treating surfaces (hardening, for example) and for various types of nuclear chemical analysis. These sources, however, tend to be very low current (μA). At slightly lower energies (tens of kilo-electron volts), but significantly higher currents (50 A), are the ion sources used for heating fusion plasmas.

Single-crystal fibers represent perhaps one of the most underexplored areas of material science. Despite some early interest and excitement 30 years ago, the lack of immediate applications led to a decline in research activity, and until recently, little was known about their growth behavior and properties. During the past few years single-crystal fiber research has been revived and preliminary results have stimulated considerable interest in the scientific community.

At present, the most extensive and broadly based single-crystal fiber program is at Stanford University, where the focus has been on studying fibers for optical applications. This program emerged from a desire to combine the light-guiding properties of fiber geometries with the unique physical properties of crystalline materials, as was done during the last decade for glass fiber applications. Such materials could lead to a range of novel devices with higher efficiencies than possible in bulk crystals. But single-crystal fiber growth technology may have an even broader applicability. While single-crystal fibers of semiconductor, superconductor, and high strength materials could play an important role in future device applications, an important current use for the single-crystal fiber growth technology is in preparing single crystals of a wide variety of materials for property evaluation. Fiber crystals may have much higher crystalline perfection than bulk crystals of the same composition, making them useful for studying the intrinsic properties of a material and for improving device performance. Other areas of interest which have been identified include metastable phase formation and the growth of oriented ferroic domain and multiphase structures.

As useful as classical x-ray diffraction techniques have been, the ability to obtain x-ray diffraction images with extremely short exposure rimes opens up new opportunities for materials scientists, including real-time materials process control. This article briefly describes state-of-the-art systems for obtaining extremely rapid and real-time x-ray diffraction images and gives several examples of their applications for materials process control.

Two generic electro-optical methods permit real-time viewing and recording of x-ray diffraction images. The first uses a low-intensity conventional x-ray tube source leading to a low-intensity diffraction image, which requires a high-gain electro-optical imaging system. The second uses either a high-intensity rotating anode, synchrotron, or flash x-ray source. Such a high-intensity source produces a high-intensity diffraction image, permitting use of a low-gain high-resolution electro-optical imaging system.

Figure 1 schematically shows two types of image intensifier tubes which have been most often used to view x-ray diffraction images. By cascading three individual first generation image tube stages (Figure 1a), light gains as high as several million can be obtained. The second generation microchannel-plate image intensifier tube (Figure 1b) is similar to a single-stage first generation device except for the extremely important addition of a microchannel plate.

The March meeting of the American Physical Society was held in New Orleans, March 21-25, 1988. The primary forum for APS's Division of Condensed Matter Physics, the meeting occupied the entire five days with sessions begining at 8:00 a.m., 11:00 a.m., and 2:30 p.m. Special sessions ran during dinner hours and some technical topics required evening sessions as well. According to the meeting program (an 8.5 × 11 inch book not quite 1.5 inches thick), 340 invited and 3,420 contributed abstracts were scheduled into 392 sessions. A gargantuan event to say the least. Meeting rooms were full to over-flowing for many sessions with the hottest, most pervasive topic of the week being high temperature superconductors.

Formed just three years ago, the Materials Physics Topical Group (MPTG) of the American Physical Society is thriving. At the meeting, the MPTG fielded 15 topically focused symposia comprising about 50 sessions ranging from quasicrystals to high temperature superconductors. Both invited and contributed sessions were included (the latter often featuring an invited lead-off talk). The sessions were developed through the efforts of symposium organizers in a manner not dissimilar to the way MRS symposia are run. Although there is overlap between MPTG programs and some areas treated by the APS's Condensed Matter Physics Division (CMP), this style of symposium organization is unique to MPTG.

Diluted magnetic semiconductors (DMS) are semiconducting alloys whose lattice is partly made of substitutional magnetic ions. The most extensively studied materials of this type are the alloys, in which a fraction of the group II sublattice is replaced at random by Mn. The entire family of ternary alloys, along with their crystal structure and corresponding ranges of composition, is listed in Table I. Over the past decade, these alloys have attracted a growing scientific interest because of new fundamental effects in semiconductor physics and magnetism in these materials and because of their potential applications in optical nonreciprocal devices, solid state lasers, flat panel displays, infrared detectors, and other optoelectronic applications.

The increasing popularity of this field can be attributed to the broad variety of fascinating problems offered by the study of the alloys. To begin with, there is an interest in the semiconducting properties per se — for instance, the understanding of the electronic band structure and its variation with alloy composition. As in other ternary alloys, the band parameters and the lattice constant can be “tuned” by controlling the alloy composition, opening the door to band-gap engineering and lattice matching in the context of epitaxially grown superlattices and het-erostructures. The random distribution of Mn atoms with a well-characterized antiferromagnetic Mn-Mn exchange interaction provides an ideal system for studying fundamental questions in disordered magnetism. The sp-d exchange interaction between the spins of band electrons and the localized moments of the Mn atoms constitutes a unique interplay between semiconductor physics and magnetism. This leads to unusual magneto-transport and magneto-optic phenomena such as an extremely large Faraday rotation, giant negative magneto-resistance, and a magnetic-field-induced metal-insulator transition. Finally, the potential technological importance of DMS is also being recognized. For example, the large Faraday rotation holds promise of DMS applications as optical isolators, modulators, and circulators. We will briefly introduce some of the exciting research problems offered by the study of DMS. More detailed information is available in several extensive reviews and compendia.

Over the past four decades, the growth of information processing and computational capacity has been truly remarkable, paced to a large extent by equally remarkable progress in the integration and ultra-miniaturization of semiconductor devices. And yet it is becoming increasingly apparent that currently envisioned electronic processors and computers are rapidly approaching technological barriers that delimit processing speed, computational sophistication, and throughput per unit dissipated power. This realization has in turn led to intensive efforts to circumvent such bottlenecks through appropriate advances in processor architecture, multiprocessor distributed tasking, and software-defined algorithms.

An alternative strategy that may yield significant computational enhancements for certain broad classes of problems involves the utilization of multidimensional optical components capable of modulating and/or redirecting information-carrying light wave-fronts. Such an optical processing or computing approach relies for its competitive advantage principally on massive parallelism in conjunction with relative ease of implementation of complex (weighted) interconnections among many (perhaps simple) processing elements. A wide range of computational problems exist that lend themselves quite naturally to optical processing architectures, including pattern recognition, earth resources data acquisition and analysis, texture discrimination, synthetic aperture radar (SAR) image formation, radar ambiguity function generation, spread spectrum identification and analysis, systolic array processing, phased array beam steering, and artificial (robotic) vision.

In a number of materials processes, on-line monitoring of surface finish is important to control material quality or process integrity. In rolling some sheet steel into coils, the rollers are intentionally roughened so that a specified roughness range is transferred to the sheet. Then the end product sheet can be optimally spray painted. The rollers, however, eventually wear smooth. Currently, pieces of sheet are sampled by hand and if a piece is too smooth, the coils produced since the last good sample are problematical. In automated machining it is useful to know during the cutting process whether the part will have the required surface finish. More importantly, for a large class of automated machining applications, a dull tool can be defined as one which produces a rougher part surface.

Monitoring the finish of the newly cut surface could allow a decision to be made about changing the tool. For untended machining this could provide a strategy for tool management. The strategy would be much more efficient than the alternative of changing a tool after X hours when it might have lasted 10X hours were it in the upper 10% of the life curve.

To fulfill the need for noncontact surface finish measurement, optical scattering devices have been developed to provide a surface interrogation technique. However, this technique is significantly limited for many applications because the optical beam must interact with a dry surface. This makes its application very difficult in the harsh wet environment encountered in automated machining and in some metal sheet production.

Permanent magnets have long occupied an important position in technology. Among the multitude of products using permanent magnets are televisions, telephones, computers, videocassette recorders, audio systems, household appliances, and perhaps surprisingly to many consumers, automobiles. Figure 1 illustrates the numerous magnet applications in a modern passenger vehicle. These applications include an array of dc electric motors such as the starter, heater and air conditioner blower, windshield wiper, window lift, door lock, and fuel pump motors. A fully equipped car can have more than 30 dc electric motors. Other uses include actuators, gauges, and sensors. In all these examples higher performance magnetic materials may afford the advantages of increased operating efficiency and reduction in size and weight.

One performance index or figure of merit for a permanent magnet is the energy product (BH)max, the maximum product of magnetic induction B and applied field H in the second quadrant of the B-H hysteresis curve. The so-called theoretical (BH)max, the highest energy product realizable in principle, is simply given by (4πMs)2/4, where Ms is the saturation magnetization. Progress in the development of technologically significant hard magnets has been monitored generally by improvements in (BH)max. For many years three types of materials were of commercial importance, namely, alnico, ferrite, and samarium-cobalt alloys based on either the SmCo5 or Sm2Co17 intermetallic compounds. Of these the Sm-Co magnets offer the largest energy products, on the order of 20 MGOe.

Deposition of films by sputtering was observed first in 1852 by Grove. The technique was in general use through the 1920s for preparing reflective coatings and other thin film samples. Western Electric deposited gold on wax masters for phonograph recordings. The improvement in diffusion pump technology at that time caused thermal evaporation deposition to replace sputtering.

Not till the 1950s did sputter deposition reappear… Bell Laboratories developed tantalum hybrid circuit technology using sputter deposition. Besides depositing Ta, they created a new material, Ta2N, by reactively sputtering tantalum in gas mixtures of argon and N2. Since then, these two methods, sputtering of metals and alloys and reactive sputtering of compounds, have been investigated for many applications of thin film materials.

Although the general aspects of the methods have changed little in the past 30 years, the implementations have changed significantly, particularly since the introduction of magnetron systems in the 1970s. This review will concentrate mainly on these flexible, high rate magnetron deposition systems.

The term sputtering actually applies to the physical processes by which atoms are removed from a material. Momentum is transferred from an incident, energetic particle, usually in the form of an ion, to atoms of the target material. A large number of these atoms are displaced from their normal sites in the crystal lattice, producing a disordered structure that also contains some of the incident particles, which are implanted. Some of the target atoms are displaced from the surface; if they have enough energy, they escape from the target as sputtered atoms.