BYU Physics and Astronomy

Organoplatinum(II) gemini amphiphiles with two different chain lengths are synthesized and characterized. Self-assembly at the air-water interface is investigated as a function of chain length and reduction in surface area by using Langmuir-trough techniques. The Langmuir-trough experiments lead to a conjecture that surface aggregates may be the adsorbing units. Atomic force microscopy on the transferred Langmuir- Schaefer films reveals spontaneous formation of wormlike micellar aggregates. A shear-induced transition and alignment are proposed for the observed effects.

In order to be useful as microelectromechanical devices, carbon nanotubes with well-controlled properties and orientations should be made at high density and be placed at predefined locations. We address this challenge by hierarchically assembling carbon nanotubes into closely packed and highly aligned three-dimensional wafer films from which a wide range of complex and three-dimensional nanotube structures were lithographically fabricated. These include carbon nanotube islands on substrates, suspended sheets and beams, and three-dimensional cantilevers, all of which exist as single cohesive units with useful mechanical and electrical properties. Every fabrication step is both parallel and scalable, which makes it easy to further integrate these structures into functional three-dimensional nanodevice systems. Our approach opens up new ways to make economical and scalable devices with unprecedented structural complexity and functionality.

Here we show direct polymer growth on hydrogen-terminated silicon (Si-H) as a one-step process. Si-H is immersed in a heated solution of an initiator, a monomer, and a crosslinker. The resulting polymer films are 2-15 nm thick, the thickness can be tuned by varying reaction conditions, and the polymer films are robust. Thinner films are obtained in polymer growth without crosslinker. Radicals produced by the initiator and in growing polymer chains may pluck H atoms from Si-H to make reactive dangling bonds. These in turn appear to react with monomers and crosslinkers. Crosslinkers tethered through one double bond may be grafted into polymer chains growing in solution. Surface reactivity is demonstrated by optical ellipsometry, X-ray photoelectron spectroscopy, atomic force microscopy, and wetting.

The force of adhesion was measured for single walled carbon nanotubes grown over lithographically defined silicon dioxide trenches. We varied contact lengths between the nanotubes and silicon dioxide from 230 to 850 nm. Suspended nanotubes were pushed vertically into the trenches with an atomic force microscope tip, causing them to slip along the surface. Previous work done at shorter contact lengths found that tension was constant with contact length [J. D. Whittaker , Nano Lett. 6, 953 (2006)]. This study finds that when the nanotube contact length approaches 1 mu m, the tension at which nanotubes slip begins to increase with contact length. This indicates that contact length independent adhesion is a uniquely nanoscale behavior. (c) 2007 American Institute of Physics.

Nanoshaving and nanografting were first introduced in 1995 and 1997. These nanoscale patterning methods have been used in a variety of applications. For example, nanoshaving, which uses an atomic force microscopy (AFM) tip to mechanically remove a molecular monolayer, has been shown to remove sexithiophene crystals physisorbed between electrical contact pads on silicon dioxide, to pattern streptavidin on gold surfaces for DNA binding, and to remove covalently attached alkyl monolayers from a silicon surface.

Laser-activation-modification of semiconductor surfaces (LAMSS) was carried out on silicon with a series of 1-alkenes. These laser spots were studied by time of flight secondary ion mass spectrometry (ToF-SIMS). The resulting spectra were analyzed using the multivariate curve resolution (MCR) method within the Automated eXpert Spectral Image Analysis (AXSIA) toolkit, and also by MCR. and cluster analysis using commercially available toolboxes for Matlab: the PLS_Toolbox and the MIA_Toolbox, respectively. AXSIA based MCR generally finds three components for the spectral images: one for the background and two for the laser-activated spots, for both the positive and negative ion images. The negative ion component spectra from the spots show increased carbon and hydrogen signals compared to oxygen. They also show reduced chlorine and fluorine (contamination) peaks. In order to compare AXSIA-MCR results from different images, the AXSIA component spectra of different spots were further analyzed by principal components analysis (PCA). PCA of all of the negative ion components shows that component I is chemically distinct from components 2 and 3. PCA of all of the positive ion components yields the same result. The loadings plots of this PCA analysis confirm that component 1 generally contains fragments expected from the substrate, while components 2 and 3 contain fragments expected from an overlayer composed of alkyl chains in the spots. A comparison of the two MCR analyses suggests that roughly the same information can be obtained from AXSIA, which is not commercially available, and the PLS_Toolbox. Cluster analysis of the data also clearly separates the spots from the backgrounds. A key finding from these analyses is that the degree of surface functionalization in a LAMSS spot appears to decrease radially from the center of the spot. Finally, a comparison of atomic force microscopy (AFM) of the spots versus the AXSIA analysis of the ToF-SIMS data produced another important result, which is that the surface morphology is only weakly correlated with the LAMSS chemistry. (C) 2007 Elsevier B.V. All rights reserved.