Electroless deposition of noble metals on silicon has applications in a wide range of fields including electronic circuitry, metal plating industry, lithography, and other fabrication techniques. In addition, studies using self-assembled monolayers (SAMs) as resists for electroless deposition for controlled deposition have significant potential for aiding advancement in the fields of nanoelectronics, sensing applications, and fundamental studies. Herein, we discuss the development of appropriate plating solutions for controlled deposition of metallic gold and silver on Si(111) surfaces in the presence of an organic silane monolayer acting as a resist film for directed metal deposition to produce metal-monolayer hybrid surfaces while investigating microscopic plating trends. For this, plating solutions were optimized to deposit metal on bare silicon surfaces while avoiding deposition on the SAM protected areas. Trends in the electroless deposition of gold and silver on a Si(111) surface as a function of concentration of metal ions, NH4F, citric acid, sodium citrate, polyvinylpyrrolidone (PVP), and deposition time have been monitored under ambient conditions. The resulting surfaces were characterized using atomic force microscopy (AFM), and the stability of plating solutions was investigated by UV–vis spectroscopy. For both gold and silver, we observed an increase in metal deposition when the concentration of NH4F, citric acid, and deposition time increased. The addition of PVP and the pH of the solution were also shown to have a significant effect on the metal deposition. The octadecyltrichlorosilane (OTS) SAM films act as effective nanoscale resists when the NH4F concentration is reduced from typical plating conditions. In particular, NH4F concentrations from 0.02 to 0.50 M and metal ions concentrations from 0.001 to 0.020 M were found to allow deposition of metal nanostructures on a bare Si surface while preserving OTS protected areas.

Precision-controlled fabrication of metallic nanostructures is of great interest in applications such as sensing, optoelectronics, and high-capacity storage devices. However, the expense and throughput of the current methods limit the applicability of metal nanodot arrays for many of these applications. This issue is addressed by a method for generating periodic silver (Ag) and gold (Au) nanodot arrays in a straightforward, inexpensive, tunable way. Specifically, regularly placed hexagonal arrays of Ag and Au nanodots were fabricated on Si(111) surfaces via a nanosphere lithography-based approach followed by electroless deposition (ELD). Silicon surfaces with hexagonally packed nanospheres were reacted with octadecyltrichlorosilane (OTS) to form a self-assembled monolayer resist over the substrate, which leads to a hexagonal array of nanopores upon removal of the spheres. Different electroless plating solutions for Ag and Au were introduced onto the nanopore surfaces to selectively deposit metal in the nanopores, resulting in metal nanodots grown only in the nanopores, where the nanospheres were originally in contact with the substrate. Ag and Au nanodot heights can be effectively tuned from 20 to 100 nm by varying the plating time and the composition of the plating solution. Atomic force microscopy (AFM) was used to characterize the height and diameter of the nanopore and nanodot arrays along with energydispersive X-ray spectroscopy (EDS) to characterize the elemental composition distribution on the surface. This method provides control over the distance between nanodots and their size at the nanoscale with high reproducibility.

Applications such as biosensing, plasmonics, and nanoelectronics require nanoscale metal structures with controlled dimensions and placement. However, significant challenges remain in the fabrication of metal nanostructures of controlled size, shape, and placement on a solid support. Among these challenges are precise positional control at the nanoscale, flexibility and tunability in shape, and the cost and complexity of methods. This work presents the development and exploration of methods for the fabrication of copper, silver, and gold (Cu, Ag, and Au) nanostructures directly on silicon (Si) substrates through the use of atomic force microscopy (AFM)-based nanofabrication using a self-assembled monolayer (SAM) resist followed by metal deposition in the structure using electroless deposition (ELD). The importance of the role of the SAM resist layer is highlighted, as it is critical to prevent metal deposition on the areas of the substrate outside the desired pattern. We have found that octadecyltrichlorosilane (OTS) monolayers are much more robust and resistant films for the ELD process than either octadecyl SAMs, formed from alkenes on hydrogen-terminated Si, or octadecyldimethylchlorosilane (ODMS) SAM films. In addition, the patterning parameters used for the AFM-based fabrication, the ELD solution parameters, and the role of doping of Si have been explored and together the results suggest that with proper tuning of the ELD solution concentrations and the use of a robust SAM resist film, such as OTS, tunable metal nanostructures are achievable. This is demonstrated here for Cu, Ag, and Au, but the process should be adaptable to a variety of metals, as long as the redox potentials are compatible with the oxidation of Si. Importantly, this method exploits the exquisite tunability of AFM-based lithography to provide precise control over the size, shape, and position of the metal nanostructure. This provides significant advantages for prototyping of new structures, as well as fundamental investigations of the properties of such nanostructures.

The mechanism of matrix metalloproteinase-8 (MMP-8) inhibition was investigated using ellipsometric measurements of the interaction of MMP-8 with a surface bound peptide inhibitor, tether-metal abstraction peptide (MAP), bound to self-assembled monolayer films. MMP-8 is a collagenase whose activity and dysregulation have been implicated in a number of disease states, including cancer metastasis, diabetic neuropathy, and degradation of biomedical reconstructions, including dental restorations. Regulation of activity of MMP-8 and other matrix metalloproteinases is thus a significant, but challenging, therapeutic target. Strong inhibition of MMP-8 activity has recently been achieved via the small metal binding peptide tether-MAP. Here, the authors elucidate the mechanism of this inhibition and demonstrate that it occurs through the direct interaction of the MAP Tag and the Zn 2þ binding site in the MMP-8 active site. This enhanced understanding of the mechanism of inhibition will allow the design of more potent inhibitors as well as assays important for monitoring critical MMP levels in disease states.

Atomic force microscopy (AFM) tip-based fabrication has gained attention due to its unparalleled precision and control for designing nano-and microscale features. Such features have utility in applications including miniaturized electronics, biological sensing, and plasmonics. Herein, we discuss an AFM tip-based plowing approach to create patterns on the micron scale in a thin CaCO 3 nanoparticle (NP) film, deposited over a wide range of substrates. The CaCO 3 NP layer's high thermal stability allows it to be used as a resist film during high vacuum thermal evaporation of gold. After metal deposition, the NP resist film is selectively removed in aqueous solutions either by complexing with ethylenediaminetetraacetic acid or by dissolution with dilute HCl. The resulting gold metal features on surfaces were characterized by AFM and optical microscopy. The metal features were commensurate with the patterns created in the NP film. This fabrication approach was demonstrated on glass, Si, and mica, and the metal features show reasonable adhesion and stability. This patterning approach is unique in that it allows for the deposition of precisely placed metal microstructures with a defined size, shape, placement, and orientation on various substrates while using simple, easily removable resists. Salt-based resists can be removed in aqueous solutions with minimal contamination or damage to the metal features. This versatile method could be used to deposit fixed metal features on any desired substrate for applications from sensors to electronics. This is particularly useful for applications with conductive structures on optically transparent substrates, which are more challenging to fabricate with other approaches.