. Corni et al. Journal of the European Ceramic Society 28(2008)1353-1367 nm (b) Inm 212nm Fig8. Schematic of the EPD nanocell employed by Iwata et al. 73 to deposit Au dots: (a)topographical(AFM) image of Au dots deposited by EPD and(b) cross-section of the Au dot shown in image(a). (Reproduced with permission of IoP Publishing Ltd, UK) of the fibre mat, resulting in poor infiltration and low quality CNTs are now well-known and their use in a wide range of nIcI rostructure applications is spreading, with current research and develop- A further development of EPD is reactive electrophoretic ment efforts focused on expanding the application potential of deposition,that has been described by Clasen et al. 71. 72 CNTs.76-178However, it is recognized that to produce partic produce doped functional glasses. These glasses are normally ular arrangements of CNTs, individually or collectively, for a created by melting silica at 2100.C, but at this high temperature given application and to combine CNTs with other materials most of the suitable dopants evaporate. An alternative process for to form composite materials and devices, it is fundamental to that consists of adding soluble salts into a silica suspension, ceramic or metallic matrix. It is now well known that EPD is a these salts dissociate and the ions are adsorbed on the surface very convenient technique to manipulate CNT in order to form of the particles, which are then deposited by EPD producing ordered, oriented nanotubes arrays a homogeneously doped green body Shaping of a green bod To prepare a stable CNT suspension for EPD, several solvents and doping are achieved in a single step by means of reactive have been employed, including distilled water, mixtures of ace- EPD, whereas more than one step and very high temperatures tone and ethanol, and pure organic solvents such as ethanol are needed by the conventional route. isopropyl alcohol, n-pentanol, ethyl alcohol, tetrahydrofuran, Iwataetal. demonstrated that EPD can also be employed to dimethylformamide and deionised water with pyrrole. The fabricate nanostructures, such as nanomachines and components preparation of a stable suspension of CNTs, in which CNTs for nanoelectronics. This group utilized local EPD to deposit have a high s-potential and the suspension has a low ionic con- gold nanoparticles( dots)on Si surfaces from a nanopipette probe ductivity, is necessary for successful EPD. The stability of CNt filled with the deposition suspension. The nanopipette probe was suspensions, determined by s-potential measurements, has been the Epd cell and the two electrodes were a thin metal wire posi- studied mainly in aqueous and ethanol-based suspensions. Fur- tioned inside the nanopipette and a conductive surface that was thermore, it has also been shown that the presence of chargersalts practically in contact with the edge of the nanopipette(Fig 8). can play an important role in improving the adhesion of CNTs When a difference of potential was applied between them, the to substrates and in increasing the deposition rate. The salts can colloidal particles migrated toward the edge of the probe and also contribute to the stability of the suspensions by associating a were deposited on the surface. They also demonstrated that it charge to the CNT surface. This charge determines the migration was possible to modify the size of the Au dots by changing the direction of CNTs in suspension during EPD and therefore the deposition time and the voltage deposition electrode. Using different types of salts: quaternary ammonium salts, benzalkonium chloride, NiCl, Mg(NO3) 3.3.2. EPD of carbon nanotubes(CNTs) MgCl2 and NaoH a finer control can be achieved. Additionally, In the last few years the interest of the scientific commu- it is worth noting that the high aspect ratio and surface charge nity in carbon nanotubes(CNTs), both single-walled(SWCNTs) of acid-treated CNTs makes them suitable scaffolds or tem- and multi-walled (MWCNTs), has increased dramatically as plates for deposition of other nanoparticles, such as metallic and reflected by the huge number of papers published and patents oxide nanoparticles, via adsorption or nucleation at the acidic filed related to CNTs 7.8, 74 175 Many of the properties of sitesI. Corni et al. / Journal of the European Ceramic Society 28 (2008) 1353–1367 1361 Fig. 8. Schematic of the EPD nanocell employed by Iwata et al.173 to deposit Au dots: (a) topographical (AFM) image of Au dots deposited by EPD and (b) cross-section of the Au dot shown in image (a). (Reproduced with permission of IOP Publishing Ltd., UK.) of the fibre mat, resulting in poor infiltration and low quality microstructure. A further development of EPD is reactive electrophoretic deposition, that has been described by Clasen et al.171,172 to produce doped functional glasses. These glasses are normally created by melting silica at 2100 ◦C, but at this high temperature most of the suitable dopants evaporate. An alternative process for the fabrication of doped glasses is the reactive EPD technique that consists of adding soluble salts into a silica suspension, these salts dissociate and the ions are adsorbed on the surface of the particles, which are then deposited by EPD producing a homogeneously doped green body. Shaping of a green body and doping are achieved in a single step by means of reactive EPD, whereas more than one step and very high temperatures are needed by the conventional route. Iwata et al.173 demonstrated that EPD can also be employed to fabricate nanostructures, such as nanomachines and components for nanoelectronics. This group utilized local EPD to deposit gold nanoparticles (dots) on Si surfaces from a nanopipette probe filled with the deposition suspension. The nanopipette probe was the EPD cell and the two electrodes were a thin metal wire posi￾tioned inside the nanopipette and a conductive surface that was practically in contact with the edge of the nanopipette (Fig. 8). When a difference of potential was applied between them, the colloidal particles migrated toward the edge of the probe and were deposited on the surface. They also demonstrated that it was possible to modify the size of the Au dots by changing the deposition time and the voltage. 3.3.2. EPD of carbon nanotubes (CNTs) In the last few years the interest of the scientific commu￾nity in carbon nanotubes (CNTs), both single-walled (SWCNTs) and multi-walled (MWCNTs), has increased dramatically as reflected by the huge number of papers published and patents filed related to CNTs.7,8,174,175 Many of the properties of CNTs are now well-known and their use in a wide range of applications is spreading, with current research and develop￾ment efforts focused on expanding the application potential of CNTs.176–178 However, it is recognized that to produce partic￾ular arrangements of CNTs, individually or collectively, for a given application and to combine CNTs with other materials to form composite materials and devices, it is fundamental to disperse the CNTs homogeneously in the appropriate polymer, ceramic or metallic matrix. It is now well known that EPD is a very convenient technique to manipulate CNT in order to form ordered, oriented nanotubes arrays.7 To prepare a stable CNT suspension for EPD, several solvents have been employed, including distilled water, mixtures of ace￾tone and ethanol, and pure organic solvents such as ethanol, isopropyl alcohol, n-pentanol, ethyl alcohol, tetrahydrofuran, dimethylformamide and deionised water with pyrrole.7 The preparation of a stable suspension of CNTs, in which CNTs have a high -potential and the suspension has a low ionic con￾ductivity, is necessary for successful EPD. The stability of CNT suspensions, determined by -potential measurements, has been studied mainly in aqueous and ethanol-based suspensions. Fur￾thermore, it has also been shown that the presence of charger salts can play an important role in improving the adhesion of CNTs to substrates and in increasing the deposition rate. The salts can also contribute to the stability of the suspensions by associating a charge to the CNT surface. This charge determines the migration direction of CNTs in suspension during EPD and therefore the deposition electrode. Using different types of salts: quaternary ammonium salts, benzalkonium chloride, NiCl2, Mg(NO3)2, MgCl2 and NaOH a finer control can be achieved. Additionally, it is worth noting that the high aspect ratio and surface charge of acid-treated CNTs makes them suitable scaffolds or tem￾plates for deposition of other nanoparticles, such as metallic and oxide nanoparticles, via adsorption or nucleation at the acidic sites.