Electrodeposited multilayers

Nano structural materials are divided into three main types one-dimensional structures (more commonly known as multilayers) made of alternate thin layers of different composition, two-dimensional structures (wire-type elements suspended within a three-dimensional matrix), and three-dimensional constructs, which may be made of a distribution of fine particles suspended within a matrix (in either periodic or random fashion) or an aggregate of two or more phases with a nanometric grain size (these are illustrated in Fig. 17.1). 

Accurate control of microstructure ou a nanometric scale makes itpKJssible to control magnetic and mechanical properties to a hitherto unattainable degree. In particular. 

Fundamentals of Electrochemical Deposition, Second Edition. By Milan Paunovic and Mordechay Schlesinger Copyright 2006 John Wiley Sons, Inc. 

Electrodeposition of composition-modulated films was first performed by Brenner in 1939 (1) by employing two separate baths for the two components and a periodic immersion of the deposit in the two baths. This is too cumbersome a method to be adopted in practice. Deposition from a single bath with the presence of salts of the two components of the multilayer is what is desired, but there was a serious problem with the deposition of two metals from one bath. Specifically, whereas a layer of the more noble member can be deposited by choosing the potential to be between the reduction potentials of the two metals, one can expect that when the potential is set to a value appropriate for reduction of the less noble member, both will be deposited, resulting in an alloy layer rather than a pure metal. Thus, to nobody s surprise, even as recently as 1983, Cohen et al. (2), were able to deposit only a layered structure of alloys rather than pure metals. In addition they cast doubt on the possibility that a modulation cycle (the thickness of the basic layers, the periodic repetition of which 

In 1984, Tench and White (3) actually deposited composite structures with layer thickness periods down to hundreds of angstroms. Their nanocomposites exhibited increased tensile strength due to the harder Ni layers in a softer Cu matrix. The layers were not thin enough, however, to obtain enhancements witnessed in systems (non-electrodeposited) with layer thickness periods in the range 10 to 30 A. 

---

X-ray diffraction patterns of electrodeposited multilayered systems of sufficiently good quality to allow quantitative analysis of coherent and noncoherent strain features. 

TABLE 17.1. Cu/Ni Knoop Hardness Data for Electrodeposited Multilayers ... 

In Figure 17.9 the saturation GMR in Co/Cu electrodeposited multilayers with 20-A-layer cobalt and varying thickness of the Cu layers is given as obtained experimentally (6b) together with a fitted RKKY type of theoretical curve. For illustration... 

The studies of electrodeposited multilayer materials to date show clearly that electrodeposition is a feasible technique for the production of thin multilayered materials in systems that from an electrochemical standpoint are adaptable to the pulsed deposition technique. 

It is also possible to electrodeposit multilayers in cylindrical pores of a suitable etched polymer membrane. Typically, wires with diameters of about 100 nm and length of 5-10 fim can be obtained. The deposition cycles are similar to the ones described above. Magnetoresistance [this is a term describing the relative decrease (increase) in electrical resistance of a material when subjected to a magnetic field longitudinally (transversely) to the current flow] measurements with the current perpendicular to the planes are possible. In addition, giant magnetoresistance (GMR defined below) effects may be observed as well. 

Ross, C. A. 1994. Electrodeposited multilayer thin films. Annu. Rev. Mater. Sci. 24 159-188. 

---