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Influence of the magnetic field and magnetoresistance on the electrodeposition of Ni nanocontacts in thin films and microwires
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) 2436–2438
Influence of the magnetic field and magnetoresistance on the electrodeposition of Ni nanocontacts in thin films and microwires N.D. Nikolic, Hai Wang, Hao Cheng, C.A. Guerrero, N. Garcia* Laboratorio de Fisica de Sistemas Pequenos y Nanotecnologia, Consejo Superior de Investigaciones Cientificas Calle Serrano, 144, Madrid E-28006, Spain
Abstract We present a study of electrodeposition of Ni nanocontacts in thin film and microwires gaps under an external applied magnetic field. The study is performed in comparison with electrodeposition of Cu that is not a magnetic material and therefore one can obtain conclusion from the electrodeposited structures on the effect of the magnetic field on the magnetic properties of the deposition. We show that indeed there is a magnetohydrodynamic effect. But we also show, what is more important, that the magnetic properties of the deposit are crucial for the deposited structure. In particular, for this case, the magnetoresistance plays a dominant role. r 2003 Elsevier B.V. All rights reserved. PACS: 68.35. p; 73.40. c; 75.70. i; 81.15. pq Keywords: Eletrodeposition; Nickel; Copper; Nanocontacts; Magnetic field
Morphologies of electrochemically obtained metal deposits can be strongly changed if metal electrodeposition is performed in the presence of a magnetic field [1–3]. These changes in morphology are usually and mainly ascribed to the Lorentz force [2]. During the electrolysis, this force acts on migration of ions and induces convective flow of electrolyte close to the electrode surface. This effect on the electrodeposition process is known as magnetohydrodynamic (MHD) effect. The largest effect of this force is realized when magnetic field B is applied parallel to the electrode surface (i.e. an external magnetic field is oriented perpendicular to the direction of the ion flux) [2,4]. On the other hand, when magnetic field is applied perpendicular to the electrode surface, except through the effects associated with the gravity-induced convection, no changes in the growth are a priori expected [4]. In this work, the effect of magnetic field on the electrodeposition of Ni nanocontacts was examined. Ni *Corresponding author. E-mail addresses: [email protected] (H. Wang), [email protected] (N. Garcia).
deposits obtained with, both perpendicular and parallel oriented magnetic fields, as well as, nickel deposits obtained without magnetic field were examined. Nickel was electrodeposited from the following solution: NiSO4 6H2 O—262:5 g=l; NiCl2 6H2 O— 45 g=l; H3 BO3 —37:5 g=l and coumarin—0:060 g=l: Nickel was deposited potentiostatically, at room temperature (RT), at the cathodic potentials of 1000 mV=SCE (with respect to a saturated calomel reference electrode), 1200 and 1300 mV=SCE; respectively. The counter electrode was a nickel plate parallel to cathode. Also, copper was electrodeposited from 0:2 M CuSO4 in 0:5 M H2 SO4 ; at RT and at 500 mV=SCE: The counter electrode was copper plate parallel to cathode. The deposition of nickel and copper was performed by use a bipotentiostat—model AFCBP 1, Pine Instruments Company. The electrochemical cell was plunged in a uniform magnetic field of 500 Oe; which was perpendicular or parallel to the electrode surface. The electrodeposition was performed in photolithographically patterned thin film microstructures with a micrometer gap that is closed to form a nanocontact or
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.1203
ARTICLE IN PRESS N.D. Nikolic et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 2436–2438
in the ‘‘T’’ configuration of wires that has been used previously to form nanocontacts to measure ballistic magnetoresistance (BMR) [5]. In both cases the same structures reported below are observed. At potentials of 1000 and 1200 mV=SCE; the effect of magnetic field onto nickel electrodeposition was keeping with foreseeing of MHD theory. At potential of 1300 mV=SCE; a great difference between nickel morphologies obtained without and with a perpendicular oriented magnetic field was observed (zero MHD effect was expected!). The nickel deposit obtained without magnetic field was very rough, with clearly visible clustered structure (Fig. 1a). On the other hand, the nickel deposit obtained with perpendicular oriented magnetic field was very developed arboreous beaddendritic structure (Fig. 1b). The structure of this deposit was very open, with thin branches, which terminated with as flower aggregates of nickel. A flower aggregates of nickel consisted of thin nickel branches (or filaments) which were formed of small nano-sized nickel clusters. Also, it can be seen from Fig.1 that one nickel cluster corresponds to one flower aggregate, and that a
Fig. 1. Nickel deposits (in the middle of electrode) obtained at 1300 mV=SCE: (a) without, (b) with perpendicular orientated magnetic field of 500 Oe:
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diameter of thin nickel filaments is approximately same with diameters of small nickel clusters situated on the surface of large nickel cluster. This change of the morphology is unexpected because the energy introduced by the field is just a very negligible paramagnetic effect that at RT should not account for much. However, the great change of the nickel morphology with a perpendicular oriented magnetic field can be ascribed to magnetic properties of nickel. The explanation can be given in terms of the resistance of the branched structure (i.e. filaments of deposits) due to domain wall scattering. In the case of deposits with magnetic properties (as nickel), the resistance of these filaments depends on whether a magnetic field is applied or not. In order to grow branched structure, it is necessary that the effective potential at the end of these branches to be the same as the applied one. In the absence of magnetic field, the resistance of nickel filaments formed in the initial stage of nickel electrocrystallization is too large, and the effective potential on their ends is much smaller than needed for their further growth and branches, i.e. for the electrodeposition of very developed arboreous bead-dendritic structure. For that reason, these nickel filaments mutually coalesce giving a very rough nickel structure, with very large nickel clusters which consist of small nano-sized nickel clusters. In the presence of magnetic field, the resistance of these filaments is much smaller, because the domain walls are erased and the effective potential at the end of the branches is large enough for the electrodeposition of arboreous bead-dendritic structure. The formed nickel filament do not mutually coalesce, and they continue to branch out, forming very developed dendritic structure with thin branches which terminate with as flower nickel aggregates consisted of thin nickel nanosized filaments. This is a very striking result because the small energies involved in the magnetic process can drive, in a very elegant way, the growth structure in one way or other, just due to the subtle effect of the magnetoresistance of the grown filaments, because when the field is applied the domain walls at the constrictions conforming the filaments are removed and the filament resistance diminishes drastically. These are process that should be common and may regulate delicate matters of nature and growth. It is necessary to note that a change of morphology with perpendicular oriented magnetic field is not observed in case of copper which is a paramagnetic metal and therefore no magnetoresistance effect exist under applied magnetic field. The copper deposits obtained without and with perpendicular oriented magnetic field were always arboreous bead-dendritic structures. This work has been supported by the Spanish DGICyT.
ARTICLE IN PRESS 2438
N.D. Nikolic et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 2436–2438
References [1] J.C. Shannon, Z.H. Gu, T.Z. Fahidy, J. Electrochem. Soc. 144 (1997) L314. [2] O. Devos, A. Oliver, J.P. Chopart, O. Aaboubi, G. Maurin, J. Electrochem. Soc. 145 (1998) 401.
[3] S. Bodea, L.Vignon, R. Ballou, P. Molho, Phys. Rev. Lett. 83 (1999) 2612. [4] K.M. Grant, J.W. Hemmert, H.S. White, J. Electroanal. Chem. 500 (2001) 95. [5] N. Garc!ıa, M. Mun˜oz, G.G. Qian, H. Rohrer, I.G. Saveliev, Y.-W. Zhao, Appl. Phys. Lett. 79 (2001) 4550.
Journal of Magnetism and Magnetic Materials 272–276 (2004) 2436–2438
Influence of the magnetic field and magnetoresistance on the electrodeposition of Ni nanocontacts in thin films and microwires N.D. Nikolic, Hai Wang, Hao Cheng, C.A. Guerrero, N. Garcia* Laboratorio de Fisica de Sistemas Pequenos y Nanotecnologia, Consejo Superior de Investigaciones Cientificas Calle Serrano, 144, Madrid E-28006, Spain
Abstract We present a study of electrodeposition of Ni nanocontacts in thin film and microwires gaps under an external applied magnetic field. The study is performed in comparison with electrodeposition of Cu that is not a magnetic material and therefore one can obtain conclusion from the electrodeposited structures on the effect of the magnetic field on the magnetic properties of the deposition. We show that indeed there is a magnetohydrodynamic effect. But we also show, what is more important, that the magnetic properties of the deposit are crucial for the deposited structure. In particular, for this case, the magnetoresistance plays a dominant role. r 2003 Elsevier B.V. All rights reserved. PACS: 68.35. p; 73.40. c; 75.70. i; 81.15. pq Keywords: Eletrodeposition; Nickel; Copper; Nanocontacts; Magnetic field
Morphologies of electrochemically obtained metal deposits can be strongly changed if metal electrodeposition is performed in the presence of a magnetic field [1–3]. These changes in morphology are usually and mainly ascribed to the Lorentz force [2]. During the electrolysis, this force acts on migration of ions and induces convective flow of electrolyte close to the electrode surface. This effect on the electrodeposition process is known as magnetohydrodynamic (MHD) effect. The largest effect of this force is realized when magnetic field B is applied parallel to the electrode surface (i.e. an external magnetic field is oriented perpendicular to the direction of the ion flux) [2,4]. On the other hand, when magnetic field is applied perpendicular to the electrode surface, except through the effects associated with the gravity-induced convection, no changes in the growth are a priori expected [4]. In this work, the effect of magnetic field on the electrodeposition of Ni nanocontacts was examined. Ni *Corresponding author. E-mail addresses: [email protected] (H. Wang), [email protected] (N. Garcia).
deposits obtained with, both perpendicular and parallel oriented magnetic fields, as well as, nickel deposits obtained without magnetic field were examined. Nickel was electrodeposited from the following solution: NiSO4 6H2 O—262:5 g=l; NiCl2 6H2 O— 45 g=l; H3 BO3 —37:5 g=l and coumarin—0:060 g=l: Nickel was deposited potentiostatically, at room temperature (RT), at the cathodic potentials of 1000 mV=SCE (with respect to a saturated calomel reference electrode), 1200 and 1300 mV=SCE; respectively. The counter electrode was a nickel plate parallel to cathode. Also, copper was electrodeposited from 0:2 M CuSO4 in 0:5 M H2 SO4 ; at RT and at 500 mV=SCE: The counter electrode was copper plate parallel to cathode. The deposition of nickel and copper was performed by use a bipotentiostat—model AFCBP 1, Pine Instruments Company. The electrochemical cell was plunged in a uniform magnetic field of 500 Oe; which was perpendicular or parallel to the electrode surface. The electrodeposition was performed in photolithographically patterned thin film microstructures with a micrometer gap that is closed to form a nanocontact or
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.1203
ARTICLE IN PRESS N.D. Nikolic et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 2436–2438
in the ‘‘T’’ configuration of wires that has been used previously to form nanocontacts to measure ballistic magnetoresistance (BMR) [5]. In both cases the same structures reported below are observed. At potentials of 1000 and 1200 mV=SCE; the effect of magnetic field onto nickel electrodeposition was keeping with foreseeing of MHD theory. At potential of 1300 mV=SCE; a great difference between nickel morphologies obtained without and with a perpendicular oriented magnetic field was observed (zero MHD effect was expected!). The nickel deposit obtained without magnetic field was very rough, with clearly visible clustered structure (Fig. 1a). On the other hand, the nickel deposit obtained with perpendicular oriented magnetic field was very developed arboreous beaddendritic structure (Fig. 1b). The structure of this deposit was very open, with thin branches, which terminated with as flower aggregates of nickel. A flower aggregates of nickel consisted of thin nickel branches (or filaments) which were formed of small nano-sized nickel clusters. Also, it can be seen from Fig.1 that one nickel cluster corresponds to one flower aggregate, and that a
Fig. 1. Nickel deposits (in the middle of electrode) obtained at 1300 mV=SCE: (a) without, (b) with perpendicular orientated magnetic field of 500 Oe:
2437
diameter of thin nickel filaments is approximately same with diameters of small nickel clusters situated on the surface of large nickel cluster. This change of the morphology is unexpected because the energy introduced by the field is just a very negligible paramagnetic effect that at RT should not account for much. However, the great change of the nickel morphology with a perpendicular oriented magnetic field can be ascribed to magnetic properties of nickel. The explanation can be given in terms of the resistance of the branched structure (i.e. filaments of deposits) due to domain wall scattering. In the case of deposits with magnetic properties (as nickel), the resistance of these filaments depends on whether a magnetic field is applied or not. In order to grow branched structure, it is necessary that the effective potential at the end of these branches to be the same as the applied one. In the absence of magnetic field, the resistance of nickel filaments formed in the initial stage of nickel electrocrystallization is too large, and the effective potential on their ends is much smaller than needed for their further growth and branches, i.e. for the electrodeposition of very developed arboreous bead-dendritic structure. For that reason, these nickel filaments mutually coalesce giving a very rough nickel structure, with very large nickel clusters which consist of small nano-sized nickel clusters. In the presence of magnetic field, the resistance of these filaments is much smaller, because the domain walls are erased and the effective potential at the end of the branches is large enough for the electrodeposition of arboreous bead-dendritic structure. The formed nickel filament do not mutually coalesce, and they continue to branch out, forming very developed dendritic structure with thin branches which terminate with as flower nickel aggregates consisted of thin nickel nanosized filaments. This is a very striking result because the small energies involved in the magnetic process can drive, in a very elegant way, the growth structure in one way or other, just due to the subtle effect of the magnetoresistance of the grown filaments, because when the field is applied the domain walls at the constrictions conforming the filaments are removed and the filament resistance diminishes drastically. These are process that should be common and may regulate delicate matters of nature and growth. It is necessary to note that a change of morphology with perpendicular oriented magnetic field is not observed in case of copper which is a paramagnetic metal and therefore no magnetoresistance effect exist under applied magnetic field. The copper deposits obtained without and with perpendicular oriented magnetic field were always arboreous bead-dendritic structures. This work has been supported by the Spanish DGICyT.
ARTICLE IN PRESS 2438
N.D. Nikolic et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 2436–2438
References [1] J.C. Shannon, Z.H. Gu, T.Z. Fahidy, J. Electrochem. Soc. 144 (1997) L314. [2] O. Devos, A. Oliver, J.P. Chopart, O. Aaboubi, G. Maurin, J. Electrochem. Soc. 145 (1998) 401.
[3] S. Bodea, L.Vignon, R. Ballou, P. Molho, Phys. Rev. Lett. 83 (1999) 2612. [4] K.M. Grant, J.W. Hemmert, H.S. White, J. Electroanal. Chem. 500 (2001) 95. [5] N. Garc!ıa, M. Mun˜oz, G.G. Qian, H. Rohrer, I.G. Saveliev, Y.-W. Zhao, Appl. Phys. Lett. 79 (2001) 4550.