Formation of Si Nanorods and Discrete Nanophases by Axial Diffusion of Si from Substrate into Au and AuPt Nanoalloy Nanorods.

Interdiffusion between Si substrate and nanorod arrays of Au, Pt, and AuPt nanoalloys is investigated at temperatures lower than the AuSi eutectic temperature. When the nanorod is pure Au, Si diffusion from the substrate is very rapid. Au atoms are completely replaced by Si, converting the nanostructure into one of Si nanorod arrays. Au is diffused out to the substrate. The Au nanorod arrays on Si are unstable. When the nanorod is pure Pt, however, no diffusion of Si into the nanorod or any silicide formation is observed. The Pt nanorods are stable on Si substrate. When the nanorods are an alloy of AuPt, interesting interactions occur. Si diffusion into the nanorods is rapid but the diffusing Si readily reacts with Pt forming PtSi while Au diffuses out to the substrate. After annealing, nanophases of Au, Pt, PtSi, and Si may be present within the nanorods. When the Pt content of the alloy is low (12 at%) all Pt atoms are converted to silicide and the extra Si atoms remain in elemental form, particularly near the tip of the nanorods. Hence, the presence of Au accelerates Si diffusion and the ensuing reaction to form PtSi, a phenomenon absents in pure Pt nanorods. When the Au content of the alloy is low, the Si diffusion would cease when all Au atoms have diffused out of the nanorod, thereby arresting the silicide formation resulting in excess Pt in elemental form within the nanorod. This is a technique of making Si nanorods with and without embedded PtSi nanophase consisting of heterojunctions which could have unique properties.

Nanocomposite Films of Laponite/PEG-Grafted Polymers and Polymer Brushes with Nonfouling Properties.

We explore the suitability of nanocomposite thin films based on laponite nanomaterial and grafted antiadhesive polymers as transparent nonfouling surfaces. For this purpose, two polymers were chosen: a linear poly(ethylene glycol) (PEG) silane, 2-[methoxy(polyethyleneoxy)propyl]-trimethoxysilane), and thermoresponsive poly(oligo ethylene glycol)-methyl ether-methacrylate (POEGMA) brushes. PEG silane was grafted on the laponite nanoparticles in solution yielding homogeneous and transparent thin films via a dip coating procedure on glass and silicon substrates. POEGMA was grafted on laponite-(3-Aminopropyl)trimethoxysilane (APTMS) nanocomposite films that were processed similarly to PEG-silane using atom transfer radical polymerization (ATRP). Film characterization with, among others, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM) attests to successful grafting of the polymers to the laponite nanoparticles. In particular, evidence of basal plane expansion of laponite with increasing silane concentration are obtained using XRD, while patent morphological changes are revealed with AFM. The results are discussed in terms of the different grafting sites on laponite and compared with literature. While LP-PEG-silane is easily applied to a surface from a precursor solution via a dip coating procedure LP-APTMS-OEGMA requires lots more chemicals, a thorough control of reaction parameters, and longer reaction time in order to generate films with the desirable properties. We therefore also addressed the antifouling properties of the films. These were tested together with control samples of bare glass and laponite thin films for 30 days in an algae container. More tests were conducted with fibroblast cell cultures. Our preliminary results show that grafting of PEG containing polymers and polymer brushes alters the properties of the laponite films from fouling to nonfouling surfaces. As a first estimate, the adhesion of particles (diatoms, algae, etc.) to surfaces is reduced by approximately 85% in the case of LP-PEG-silane and up to 92% in the case of LP-APTMS-POEGMA, in comparison to the control surfaces. Furthermore, practically no cell adhesion on such surfaces could be observed.

Understanding and Shaping the Morphology of the Barrier Layer of Supported Porous Anodized Alumina on Gold Underlayers.

Large-area ordered nanorod (NR) arrays of various functional materials can be easily and cost-effectively processed using on-substrate anodized porous aluminum oxide (PAO) films as templates. However, reproducibility in the processing of PAO films is still an issue because they are prone to delamination, and control of fabrication parameters such as electrolyte type and concentration and anodizing time is critical for making robust templates and subsequently mechanically reliable NR arrays. In the present work, we systematically investigate the effects of the fabrication parameters on pore base morphology, devise a method to avoid delamination, and control void formation under the barrier layer of PAO films on gold underlayers. Via systematic control of the anodization parameters, particularly the anodization current density and time, we follow the different stages of void development and discuss their formation mechanisms. The practical aspect of this work demonstrates how void size can be controlled and how void formation can be utilized to control the shape of NR bases for improving the mechanical stability of the NRs.