Perpendicular electrodeposited

The Russell group has applied the template synthesis approach to nanoporous films generated from UV-treated PS-fo-PMMA copolymers [43, 147,233,235,241], which were pre-aligned perpendicular to the substrate by an electric field. Through direct current electrodeposition, they fabricated high-density vertical arrays of ferromagnetic cobalt nanowires (Fig. 10a) [43]. Through subsequent work, they also demonstrated the successful replication... 

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. 

The mechanism of electrodeposition or electrocrystallization28 29 involves, as a first step, the reduction of a cation on the substrate surface (aided by an applied potential or current) to form an adatom, and its migration over the surface to an energetically favourable site. Other atoms of the electrodeposit aggregate with the first, forming the nucleus of a new phase. The nucleus grows parallel and/or perpendicular to the surface. Clearly, a number of nuclei can form and grow on the surface. When all the electrode surface is covered with at least a monolayer, deposition is on the same metal rather than on a different metal substrate. As is to be expected, the formation of the first layers determines the structure and adhesion of the electrodeposit. 

Subsequently, Stamm and coworkers [184-186] used PS-fo-P4VP diblock copolymers in combination with 2-(4-hydroxybenzeneazo)benzoic acid (HABA, Scheme 7). Thin films with cylindrical nanodomains of the P4VP-HABA complexes in a PS matrix were produced. The ahgnment of the cylinders could be switched upon exposure to vapors of different solvents from parallel to perpendicular (Fig. 25). Extraction of HABA resulted in nanoporous membranes with hollow channels of 8 nm (Fig. 26). The channels were filled with Ni clusters via the electrodeposition method to fabricate an ordered array of metalhc nanodots. 

Niklas [42] discusses edge weaknesses in nickel electroformed sieves due to acute angle comers. Additives used during photo-etching increases these defects [43] Stork [44] also describe sieve preparation by electrodepositing a thin metal skeleton on to a substrate, removal of the skeleton from the substrate, followed by deposition of two or more layers of metal on both sides of the substrate. Additives encourage growth perpendicular to the surface of the skeleton. 

The increase in the brightness of metals electrodeposited in the presence of ultrasound is thought to be due to the shock waves that are generated by cavitation these waves not only harden the surface and remove hydrogen bubbles, but also break off any perpendicular growths, such as dendrites. This in turn leads to the high surface quality and brightness which has been observed with copper electrodeposits [81]. 

Evans PR, Yi G, Schwarzacher W (2000) Current perpendicular to plane giant magnetoresistance of multilayered nanowires electrodeposited in anodic aluminum oxide membranes. Appl Phys Lett 76 481 83... 

Electrodeposition of Electronic Materials for Applications in Macroelectronic- and Nanotechnology-Based Devices, Fig. 1 3-D AFM image of electrodeposited CdS showing highly oriented and closely packed nanorods standing perpendicular to the substrate... 

The method makes use of the tendency of a metal foil to bend when it is oxidised unilaterally, i.e. on one side only, and has been developed from the method used by Stoney to measure stresses in electrodeposits, as long ago as 1909. There are important problems in the translation of the technique to oxidation studies. Firstly, it is difficult to completely arrest oxidation on the Inert side of the testpiece. The problems of diffusion across a barrier layer of electrodeposited or vapour-deposited metal for a long time restricted its use to low temperatures, e.g. Ta at 350-550 C Nb at 425 C" and Cu at 200-400 C, but recently Pawel and Cathcart have reported the use of Al-3Au evaporated layers which, on uranium alloys, will enable temperatures of up to 800°C to be used" . Secondly, there is an interpretive difficulty since although there are two stress systems, acting at right angles in the plane of the oxide, a strip (or even a disc) generally bends in a plane perpendicular to only one of them . 

Very often, the applied electric field induces reorientation of anisotropic particles and buildup of aligned particulates. This was elegantly demonstrated by Walcarius et al. [45] for the electrodeposition of perpendicular orientation of mesoporous electrodeposit on electrodes. 

Electrodeposition into templates. A most often used approach to create aligned nanostructures (such as nanowires, -tubes and similar, perpendicular to the electrode) is deposition into a nanoporous template. Such templates may be - as illustrated in Fig. 1 - porous alumina, self-assembled polystyrene beads, ion track-etch channels. Both cathodic and anodic electrodeposition of structures can be achieved, such as metal oxides, sulfides, or tellurides, as well as polymers. " °°... 

Surfactants have also been used as a soft template for the electrochemical deposition of mesoporous silica films. Walcarius et al [28] demonstrated the elec-trochemically assisted self-assembly of surfactant-templated silica thm films on various conductive substrates (Au, Pt, glassy carbon, ITO, and Cu). The films were highly ordered and homogeneous over wide areas. Figure 12.10 shows the TEM images of the electrodeposited mesoporous silica films. Hexagonal pores are seen to be well ahgned perpendicular to the surface. It is believed that the cathodic potential applied on the substrate not only drove the sol-gel film... 

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