Nanostructures are becoming increasingly important for technology and basic science. 1 Fabrication techniques currently employed for material deposition include low-pressure chemical vapor deposition (LPCVD), 2 laser-assisted chemical vapor deposition (LCVD), 3 plasma-enhanced chemical vapor deposition (PECVD), 4,5 ultraviolet stereo lithography, 6 spinning, 7 dipping, 8 spraying, 9 and electrodeposition. [10][11][12][13][14][15] Electrodeposition methods have many advantages over the other stated techniques and are attractive, as they are simple, inexpensive, reproducible, and damage-free. In addition, many materials can be deposited using electrodeposition, including metals, metal alloys, conducting polymers, and semiconductors with essentially no limitations on the size of the substrate or on the thickness of the deposited material. 16 Scanning probe microscopy (SPM) such as scanning tunneling microscopy (STM), 17 atomic force microscopy (AFM), 18 and scanning electrochemical microscopy (SECM) 19 has been widely used as a tool for surface imaging with atomic resolution. Furthermore, creation of structures using SPM has lately attracted considerable attention. 20-23 Using SPM for surface modification has advantages in that the modification process can be followed in real time and submicrometer resolution can be achieved. 24-25 SPM-based nanofabrication has potential uses in applications such as high-density information storage, high-resolution lithography, and production of nanoscale integrated chemical systems and electronic devices.Several groups have employed SPM to deposit metal and polymer microstructures. [28][29][30][31] Bard et al. 32 used the SECM to deposit different metals (e.g., Cu, Ag, Au, Pd) on polymer-coated substrates, whereas Shahat and Mandler et al. used the same technique to deposit Ni(OH) 2 structures 33 from aqueous solutions by changing the pH locally on the substrate and gold patterns by the controlled dissolution of a gold ultramicroelectrode (UME) tip. 34 Wipf and Zhou 35 used the "microreagent" SECM mode to deposit conducting polyaniline patterns on different substrates. Lagraff and Gewirth 36 employed the tip of an AFM to direct the growth of nanoscopic copper protrusions, whereas Madden and Hunter used a tip-directed scheme to deposit several micrometer-scale nickel structures. 25 In tip-directed localized deposition, 32 a faradaic current flows through the solution between a UME tip and a metal substrate electrode all immersed in an ionically conducting electrolyte when a bias voltage is applied between these two electrodes. If reducible metal ions are present in the electrolyte (e.g., Cu 2ϩ ions) and the substrate electrode potential is negative with respect to the tip electrode, then the passage of the faradaic current results in the deposition of metal on the substrate and an oxidation process at the tip. The magnitude of the faradaic current is kept constant by means of a conventional feedback control that monitors the current and adjusts the interelectrode spacing according...

Adding to the efforts spent to establish localized electrochemical deposition (LECD) as a standard fabrication process; this paper presents an experimental investigation and theoretical modelling of shape formation of high aspect ratio columns and lines fabricated by LECD. The proposed model suggests that transport of depositing ions leading to deposit formation is mainly dominated by migration forces. The deposition model is verified by numerical simulation which utilizes electric field calculation by a boundary element method and a progressive boundary update approach to determine the evolution of deposition profiles. Simulation results are compared against images of copper columns obtained at different formation stages during the deposition process. Both results are in agreement, which demonstrates the potential and capabilities of the proposed model and simulation procedures as an analysis tool to aid in characterizing the deposition process and resulting structures, as well as the understanding of the dynamics and factors influencing object formation in LECD.

Development issues required to advance localized electro-deposition for integration with commercial fabrication techniques are presented through both experimental demonstrations and theoretical modelling of the various aspects of the process. The process is a potential candidate solution for challenges facing current fabrication technologies, and definitely has great potential for post-processing and rapid prototyping applications, especially when considering high aspect ratio structures. The various interactions determining the process mechanisms and rate are well understood through mass transfer modes as demonstrated by the agreement between simulation and experimental results of the deposition profile evolution under various process conditions. The process compatibility for integration with current commercial fabrication processes as well as automation is high. Up-to-date demonstration of the process resolution suggests suitability for many applications requiring structures with micron and possibly submicron scale dimensions, but would require further development to achieve nanometre resolution. It is concluded that the achievement of foreseen developments requires collaboration of interdisciplinary efforts.

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Adding to the efforts spent to establish localized electrochemical deposition as a standard fabrication process, this paper presents an experimental investigation and theoretical modeling of shape formation of high aspect ratio columns and lines fabricated by localized electrochemical deposition. The proposed model suggests that transport of depositing ions leading to deposit formation is dominated mainly by migration forces. The deposition model is verified by numerical simulation which utilizes electric field calculation by a boundary element method and a progressive boundary update approach to determine the evolution of deposition profiles. Simulation results are compared against images of copper columns obtained at different formation stages during the deposition process. Both results are in agreement, which demonstrates the potential and capabilities of the proposed model and simulation procedures as an analysis tool to aid in characterizing the deposition process and resulting structures, as well as the understanding of the dynamics and factors influencing object formation in localized electrochemical deposition. © 2003 The Electrochemical Society. All rights reserved.