BYU Physics and Astronomy

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.

We describe the preparation of homogeneous olefin-terminated monolayers on scribed silicon made from 1,9-decadiene, and mixed monolayers with varying degrees of olefin termination prepared from 1,9-decadiene and 1-decene or 1-octene, and their subsequent reactions with bromine, osmium tetroxide, dicholorocarbene, and Grubbs' catalyst. Each of these reagents contains a heteroatom, which allows straightforward monitoring of the surface reactions by X-ray photoelectron spectroscopy (XPS). Surface reactions of mixed monolayers made from 1,9-decadiene and 1-octene are consistently more efficient than surface reactions of mixed monolayers made from 1,9-decadiene and 1-decene, presumably because of steric effects. After chemisorbtion of Grubbs' catalyst, ring-opening metathesis polymerization (ROMP) of norbornene is demonstrated. The kinetics of Grubbs' catalyst adsorption and of polynorbornene growth is monitored by XPS and time-of-flight secondary ion mass spectrometry (ToF-SIMS). A principal components analysis (PCA) of the ToF-SIMS data is presented. Autoscaling is shown to be a relatively ineffective preprocessing method for this data. Polynorbornene features on patterned substrates effectively resist and direct the electroless deposition of copper.

In this letter, we report a new and extremely rapid technique for surface modification, which we term laser activation modification of semiconductor surfaces or LAMSS. This method consists of wetting a semiconductor surface ( e. g., silicon or germanium) with a reactive compound and then firing a highly focused nanosecond pulse of laser light through the transparent liquid onto the surface. The high peak power of the pulse at the surface activates the surface so that it reacts with the liquid with which it is in contact. Evidence for functionalization of the spots is given by ToF-SIMS imaging and small-spot XPS.