Silicon Chemical Vapor Infiltration

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: Indium-doped CdSe nanoparticles have been synthesized and characterized. Their light absorption, photoluminescence, and structure are similar to undoped Use nanoparticles. The greater part of the In associated with the nanoparticles is removed when the nanoparticles undergo ligand exchange by pyridine. As observed with undoped nanoparticles, a ZnS capping layer on the indium-doped nanoparticles results in enhanced nanocrystal photoluminescence. Also, the ZnS cap enhances the retention of In by the nanoparticles. Elemental analysis shows ligand exchange causes CdSe to be lost and capping with ZnS results in the loss of Se. We conclude that In-doped nanoparticles have most of the In on their surface, capping helps the nanoparticles retain the In, and they do not have altered electronic properties. (c) 2006 Elsevier Inc. All rights reserved.