The following article is an edited transcript of a talk presented in Symposium X—Frontiers of Materials Research at the 2002 Materials Research Society Fall Meeting in Boston on December 2, 2002. From Bessemer steel used on the first motorized bicycle in 1871 to sintered aluminum ceramic composites and TiN thin-film coatings used on standard production machines today, motorcycles have been at the forefront of the use of high-performance materials. Thanks to developments in materials technology, relatively inexpensive mass-produced motorcycles are now capable of achieving speeds of >190 mph.

We have used in situ polar Kerr effect measurements to study the magnetic anisotropy of X/Co/Y sandwich structures grown by MBE on Cu(111) buffers, where X and Y are variable thicknesses of Au. For fixed values of Y and in the case of an underlayer wedge, e.g. variable X value, we have found a sharp minimum in both coercive field and perpendicular anisotropy at ≈1 atomic layer of the Au underlayer. This anisotropy behavior is opposite to that of an Au overlayer deposited on a Co film, i.e. variable Y and fixed X.

We have used Molecular Beam Epitaxy (MBE) to successfully grow films that are predominantly IrSi3 on both Si(111) and Si(100) substrates by codeposition of Si and Ir in a 3:1 ratio. Bragg-Brentano and Seemann-Bohlin x-ray diffraction reveal that polycrystalline IrSi3 films form as low as 450 °C. This is the lowest temperature yet reported for growth of this iridium silicide phase. These x-ray diffraction techniques, along with Transmission Electron Microscope (TEM) diffraction and in situ Low Energy Electron Diffraction (LEED), show that at higher deposition temperatures codeposition can form IrSi3 films on Si(111) that consist predominantly of a single epitaxial growth orientation. Ion beam channeling and x-ray rocking curves show that the epitaxial quality of IrSi3 films deposited on Si(111) is superior to that of IrSi3 films deposited on Si(100). We also present evidence for several new epitaxial IrSi3 growth modes on Si(111) and Si(100).

We have used in situ polar Kerr effect measurements to study the magnetic coercivity and anisotropy of MBE-grown Pd (111) /Co/X and Au (111) /Co/X trilayers, where χ is the nonmagnetic noble or transition metal overlayer Ag, Cu or Pd. Polar hysteresis curves were Measured in situ for systematically varied Co and overlayer thicknesses 2 Å ≤ tco ≤ 20 Å and 0 Å ≤ tx ≤ 50 Å. We find the coercivity and total anisotropy display a strongly peaked perpendicular contribution at ∼1 atomic layer (2 Å) non-Magnetic Metal coverage. For Cu, where the effect is strongest, the total anisotropy energy rapidly decreases by a factor of 3 from its peak value after a total coverage of ∼2 atomic layers (4 A) of Cu.

In 1925, P. Auger first observed the so-called Auger electrons in a Wilson cloud chamber. He explained this occurrence as being due to a radiationless transition in atoms excited by a primary x-ray photon source. In 1953, Lander first pointed out that Auger electrons arising from solid samples can be detected in the energy distribution curve of secondary electrons from surfaces subjected to electron bombardment. Moreover, low-energy Auger electrons (∼1 keV kinetic energy) can escape from only the first several atomic layers of a surface since they are strongly absorbed by even a monolayer of atoms. Thus Auger electron spectroscopy (AES) possesses high surface sensitivity. This is one characteristic that makes AES very useful for the study of thin films. For such applications, an important development in AES occurred when Harris showed that the sensitivity of the detection of Auger electrons can be improved by differentiating the electron energy distribution curve with respect to the energy. Furthermore, Weber and Johnson demonstrated that, provided the Auger line profile does not change, the peak-to-peak height in the differentiated energy distribution curves is proportional to the Auger current in the peak. Therefore, in addition to its surface sensitivity, AES also can be used for quantitative studies of thin films.

Like AES, x-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that uses the energy distribution of electrons ejected from a thin film for quantitative analysis. However, in many ways the information provided by AES and XPS is complementary.

A panel discussion on interface roughness was held at the Fall 1992 Materials Research Society meeting. We present a summary of the results presented by the invited speakers on the application and interpretation of X-ray reflectivity, atomic force microscopy (AFM), scanning tunneling microscopy (STM), photoluminescence and transmission electron microscopy. A transcript of the moderated discussion is provided in the final section.

Multilayer thin film structures for reflecting soft x-rays are now being fabricated in a number of laboratories. However, understanding of. the optical properties of these structures is presently limited by lack of knowledge of the microstructure of the layers, as well as of the details of the interfaces. In this paper we present results from our studies of multilayers grown by molecular beam epitaxy (MBE), characterized in situ by reflection high energy electron diffraction (RHEED), low energy electron diffraction (LEED), Auger, and x-ray photoelectron spectroscopy (XPS), and characterized ex situ by scanning tunneling microscopy (STM), transmission electron microscopy (TEM), x-ray diffraction, and Rutherford back scattering (RBS). In the case of Mo/Si multilayers, we observe the formation of an amorphous interfacial silicide, which can have a positive effect on the performance of these evaporated multilayer mirrors. We observe a contraction in the period of these multilayers as the deposition temperature is raised from 50 °C to 250 °C, corresponding to an increase in the thickness of the interfacial silicide. This contraction indicates that the silicide is more dense than the average atomic density of its components. We also discuss Ag/B and Pd/B multilayers, which have very similar theoretical performance. However, due to differences in the multilayer structures formed, the actual performance of multilayers made from these materials is radically different. The structural differences originate from different growth modes for Ag and Pd on B.

The ability to study, and to some extent control, the magnetic properties of surfaces and interfaces is an extremely interesting development in the field of magnetism. Along with experimental advances in techniques to accurately prepare magnetic structures by such methods as sputtering and molecular beam epitaxy (MBE) have been theoretical and computational advances in the ability to calculate properties of realistic model systems. At the same time, increasingly sophisticated characterization techniques have become available (e.g., intense synchrotron sources, pulsed sources for magnetic neutron scattering, polarized electron microscopy, scanning tunneling microscopy, etc.), which enable sample characterization at a level not before possible.

In recent years, the study of magnetism near surfaces and interfaces has been driven by the observation of significant differences from bulk behavior.1 An understanding of these phenomena is fundamentally important to the field of magnetism and provides the potential for technological applications.2 Although the real situation is more complicated, for the purposes of the discussion here, it is convenient to think about the causes of the observed physical effects at interfaces and in superlattices as falling into two categories: “dimensionality effects,” due to the reduced coordination of the magnetic atoms; and “substrate effects,” due to interactions between the differing materials at an interface. An ultrathin film on an insulator, or the free surface of a bulk crystal, are examples of the first category. However, the magnetic atoms at an interface between two different materials are affected both by the reduced number of similar neighboring atoms (i.e., the dimensionality) and by the crystal and electronic structure of the neighboring layer (i.e., the substrate).

Using magnetically enhanced dc-triode sputtering we have grown metallic multilayers of Ag/Pd and Cu/Pd with modulation wavelengths A ranging from 10 Å to 120 Å. The Ag/Pd films were prepared with two different thickness ratios of silver to palladium (1:1 and 3:1) while the Cu/Pd films all were 1:1. We observed in the Ag/Pd films that the variation with A of the (111) lattice spacing dav in the growth direction is less than 0.5%, independent of the composition. However, these films exhibited enhancements in the Rayleigh sound velocity vR of up to 22% for the 1:1 samples and 13% for the 3:1 Ag/Pd samples respectively as A decreased. The Cu/Pd films showed a slight systematic dependence of dav on A, although its variation was only approximately 0.7%. A softening in vR of up to 7% for the Cu/Pd samples was observed.

Magnetic multilayers consisting of alternating layers of cobalt and either copper or palladium have been made by magnetically enhanced dc triode sputtering onto single crystal sapphire substrates. The structural, magnetic and magnetooptic properties of these multilayers have been studied. Both multilayer systems have fcc crystalline layering. We find the magnetization in the Cu/Co multilayers is due to the cobalt layers, whereas the magnetization in the Pd/Co system comes from both cobalt and palladium layers. Also, the magnetic anisotropy of the two systems is different. The Cu/Co multilayers have an inplane easy axis of magnetization due to the strong shape anisotropy. The Pd/Co multilayers exhibit a perpendicular easy axis of magnetization for thin cobalt layers due to a large interface anisotropy contribution. The Kerr rotation of the Cu/Co and Pd/Co multilayers has been studied to determine the effect of multilayer structure on magneto-optic properties. The results of the magnetooptic characterization of these multilayer systems are presented here.

Materials with anisotropies giving rise to perpendicular magnetization are important for optical data storage applications. However, the microscopic origin of the anisotropies is not well understood. It is now widely recognized that understanding the origin of surface and interface anisotropies is one of the most important problems in magnetism. Ultra-high vacuum deposition techniques allow the sequential deposition of layers of several elements with great regularity, and little interdiffusion and contamination at the interfaces. The microstructure of the resultant multilayer materials can vary from amorphous, or polycrystalline with only short range order, to high quality superlattices with long range structural coherence in all three dimensions. This paper gives an introduction to rare-earth/transitionmetal and transition-metal/transition-metal multilayers and superlattices. Sputtering and Molecular Beam Epitaxy (MBE) processes used to grow these materials are then described, as are the in situ and ex situ characterization techniques used to determine their electronic and physical structure, and to measure their magnetooptic properties. Some of the magnetic and magneto-optic properties of materials produced by sputtering and MBE related to optical data storage are discussed.

The Rayleigh acoustic waves of sputter-deposited Cu/Co, Ag/Pd and Cu/Pd sup-erlattice films were studied using Brillouin scattering. All three of these systems are fcc/fcc superlattices. The dependence of the Rayleigh wave velocities for these films on the superlattice modulation wavelength is discussed.

Superlattice superconductors exhibit behavior different from other “homogeneous” superconductors because of their layered structures. Sputtering has proved to be an excellent technique for producing such multilayered systems. Also, systems naturally having layered structures, such as the new high-Tc materials, can be fabricated by sputtering. Here we describe the preparation of superconducting superlattices by dc triode sputtering and techniques useful for characterizing them. In particular, we discuss Mo/Ta superconducting superlattices and high Tc thin films of YBa2Cu3O7-x.

Since the coherence length is of order 50 Å to 1 μm, it is possible to alternately layer thin films of a superconductor with another material to affect the physical properties of the resulting superlattice. A brief description of our sputtering technique used to prepare superlat t ices consisting of Nb/Cu and Ta/Mo is given. Optical interferometry, x-ray diffraction and ion beam analysis techniques independently confirm that control of ±0.3% is achieved over the amount of material deposited in each layer. Results of a study of Josephson tunneling to Nb/Cu metallic super lattices are reviewed. These measurements enable a determination of the London penetration depth to be made as a function of superlattice layer thickness.

There are only a few Fe-based compounds which are superconducting since the depairing of Cooper pairs is unavoidable in the presence of an Fe moment. In Sc2Fe3Si5 and Th7Fe3, Mössbauer measurements on 57Fe show that there is no magnetism at the Fe site in either compound. The isomer shift values indicate the reason behind this identical magnetic behavior to be quite different in its electronic origin.