Growth and Reactions of SiO_x/Si Nanostructures on Surface-Templated Molecule Corrals

Abstract

Surface-templated nanostructures on the highly oriented pyrolytic graphite (HOPG) basal plane were created by controlled Cs+- or Ga+)ion bombardment, followed by subsequent oxidation at high temperature, forming molecule corrals. The corrals were then used for template growth of SiOx/Si nanostructures. We demonstrate here that, for SiOx/Si nanostructures formed in controlled molecule corrals, the amount of silicon deposited on the surface is directly correlated with the corral density, making it possible to generate patterned SiOx/Si nanostructures on HOPG. Since the size, depth, position, and surface density of the nanostructures can be controlled on the HOPG, it is possible to produce surfaces with patterned or gradient functionalities for applications in fields such as biosensors, microelectronics, and biomaterials (e.g., neuron pathfinding). If desired, the SiOx structures can be reduced in size by etching in dilute HF, and further oxidation of the nanostructures is slow enough to provide plenty of time to functionalize them using ambient and solution reactions and to perform surface analysis. Organosilane monolayers on surface-templated SiOx/Si nanostructures were examined by X-ray photoelectron spectroscopy, time-of-flight secondary ion mas spectrometry, and atomic force microscopy. Silanes with long alkyl chains such as n-octadecyltrichlorosilane (C18) were found to both react on SiOx/Si nanostructures and to condense on the HOPG basal plane. Shorter-chain silanes, such as 11-bromoundicyltrimethoxysilane (C11) and 3-mercaptopropyltrimethoxysilane (C3) were found to react preferentially with SiOx/Si nanostructures, not HOPG. The SiOx/Si nanostructures were also found to be stable toward multiple chemical reactions. Selective modification of SiOx/Si nanostructures on the HOPG basal plane is thus achievable.

Extending the Range of Controlling Protein Adsorption via Subsurface Architecture

“…Figure compares the in-depth evolution of different fragments, SiC 2 H 5 O – (Figure a), SiOH – (Figure b), and SiH 2 O 3 – (Figure c), for all samples. The presence of the SiC 2 H 5 O – fragment displays PDMS-like film properties, , whereas the SiH 2 O 3 – fragment is specific for inorganic, SiO 2 -like film structures, also providing information on cross-linking . On the other hand, the existence of SiOH – groups in the PPF is an indication for porosity as discussed earlier. − …”

“…4c), for all samples. The presence of the SiC 2 H 5 Ofragment displays PDMS-like film properties 52,53 , whereas the SiH 2 O 3fragment is specific for inorganic, SiO 2 -like film structures, also providing information on cross-linking 54 . On the other hand, the existence of SiOHgroups in the PPF is an indication for porosity as discussed earlier [55][56][57] .…”

Scanning Auger Microscopy Studies of Silane Films Grown on Plasma-Modified HOPG Surfaces

“…The applications of silanes are extremely diverse, including corrosion protection films [1,2], coupling agents and cross linkers [1,2,3,4], and corner capping agents for nanoparticle molecules such as polyhedral oligomeric silsesquioxanes (POSS) [5]. In particular, applications of silane films on carbon substrates have been reported recently, including the formation of enzyme-based biosensors [6], stabilising agents for water-soluble graphene dispersions [7], modification of graphene properties [8], incorporation of graphene [9,10] or carbon nanotubes into a polymer matrix [3,4,11,12,13], polymer-electrolyte-membrane fuel cells [9], and the formation of silicon-based nanostructures [14].…”

“…Of particular interest is the formation of the silane film on the substrate surface, and it is for this reason that propyltrimethoxysilane (PTMS) and propyldimethylmethoxysilane (PDMMS) were chosen for this study on the formation of silane films on HOPG. While there have been a range of silanes used on carbon materials for various applications [6,7,8,9,10,11,14,15], for this study, these two simple model silanes were chosen. The inert propyl chain in these molecules minimizes intermolecular interactions as much as possible while still remaining stable in solution, allowing study of the growth mechanism with minimal interference from the functional group [16].…”

“…Silane films on carbon materials have been examined previously using atomic force microscopy (AFM) [6,14], Fourier transform infrared spectroscopy (FTIR) [4,7,8,9,11,12,13], X-ray photoelectron spectroscopy (XPS) [7,8,9,13,14], transmission electron microscopy (TEM) [4,7,9,12,13], time-of-flight secondary ion mass spectroscopy (TOF-SIMS) [14], scanning electron microscopy (SEM) [8,9,14], X-ray diffraction (XRD) [8], Auger spectroscopy [15], and Raman spectroscopy [8,9]. The information from these previous studies can be combined to confirm the presence of the silane film and investigate the morphology and chemical composition of silanes on carbon materials.…”