Microelectroplating Silver on Sharp Edges toward the Fabrication of Solid-State Nanopores

Abstract

Electrodeposition of silver was investigated as a fabrication tool for constricting large (10 3 m 2 ) vias in silicon substrates while leaving a small opening in the center of the via. Silver reduction from ammoniacal silver nitrate was studied at electrodes of novel geometry, i.e., the edge of the vias, with respect to reduction potential, reduction pulse type, and pulse duration. A variety of crystal nucleation and growth patterns were observed and characterized by scanning electron microscopy. It was found that electroplated silver occluded the vias to leave open areas of less than 1 m 2 . Such occlusions might be used as restrictions in microfluidics systems, forming a type of solid-state micropore or nanopore.Electrodeposition of metals on patterned surfaces has been of interest for a number of applications including the deposition of interconnecting elements used in integrated circuits, microelectromechanical systems ͑MEMS͒ and LIGA ͑lithographic-galvanoformung-abformung, or lithography-electroplating-molding͒ processes to name examples. 1-3 In most of these applications, the goal has been to use electrodeposition to completely fill a feature that is patterned on a surface. Filling in surface features such that the deposited metal conforms to all surfaces of high-aspect-ratio topography is challenging and often requires complicated chemistry and experimental techniques. 4 The work reported here is to create a structure by use of electrodeposition to constrict a micrometer-sized opening to submicrometer size. The challenge is to attain precise control of the restriction size during electrodeposition. There have been reports of using templated electroless metal plating for partially filling in track etched membrane filters. 5 However, one feature of the templated method is it produces many pores simultaneously instead of patterning a single pore in a given location. Finer control of the deposition might be obtained using electrochemical methods.Our work is motivated by results and possible applications derived from protein nanopores. Biologically derived protein nanopores have been demonstrated for use in chemical detection and for DNA analysis. 6,7 Protein nanopores are studied while they are inserted in a lipid bilayer film. Because lipid membranes are fragile, the practical realization of these applications might require the use of an anthropogenic nanoscale pore. A stable, robust solid-state mimic might facilitate understanding of bionanopores and transport of large molecules through highly confined spaces by allowing control of the location, dimension, and composition of the pore. The challenge is to create one and only one hole, of nanometer scale in all dimensions, and in a defined location on a given substrate.A fabrication obstacle arises because many techniques which can reliably place patterns are expensive or create structures much larger than nanosize and those that create nanomaterials are often difficult to pattern down to a single feature. 8,9 One approach to resolving this discrepancy might b...

Complexing agent study via computational chemistry for environmentally friendly silver electrodeposition and the application of a silver deposit

“…During these attempts, the complexing agents for silver electroplating were widely investigated owing to their important role in the electroplating process. As a result, new complexing agents for cyanide-free silver plating baths, such as uracil, 19 ammonia, 20,21 thiourea, 22 HEDTA, 23 2-hydroxypyridine, 24,25 and ionic liquids 12,26 were proposed. However, except for a few successful cases, most of these baths still suffer from problems of instability, sensitivity to temperature or light, and relatively high toxicity and cost, as well as low deposit quality, including severe adhesion and inferior morphologies.…”

Cyclic Voltammetric Study of High Speed Silver Electrodeposition and Dissolution in Low Cyanide Solutions

“…Assuming that only Ag(CN) 2 − complexes exist in the solutions and all silver atoms come from this complex, the charge transfer of silver electrodeposition in Figure 1(a), peaks C1 and C3, can be described by (1). The difference in the free cyanide concentration in the solution has induced the change in the onset potential of electrodeposition.…”

“…However, due to stricter rules and regulations, as well as high cost of wastewater treatment, less toxic chemicals have become more favorable in most metal plating processes. Over the years, compounds such as ammonia [1,2], uracil [3], HEDTA [4], 2-hydroxypyridine [5,6], hydantoin [7], and 5,5dimethylhydantoin [8,9] have been suggested as alternatives to replace cyanides in silver plating baths. In spite of the benefits for using low toxicity cyanide-free silver plating baths, most of these electrolytes have limited practical applications in commercial manufacturing process for reasons such as relatively higher cost, low bath stability, high sensitivity to temperature and metallic contamination, low deposit quality and brightness, and poor adhesion on substrates [3,[10][11][12][13].…”

Single Nanoparticle Translocation Through Chemically Modified Solid Nanopore

“…However, currently, more attention is focused on a chemically modified nanopore which is expected to have a major impact on bioanalysis and fundamental understanding of nanoscale chemical interactions at the single-molecule level [ 16 ]. To achieve this goal, various approaches have been developed to modify the surface charge properties of nanochannels, including the deposition of metals [ 17 , 18 ], oxides [ 19 , 20 ], and various organic modifications [ 21 , 22 ]. More recently, the chemically modified nanopores have been reported.…”