F. H. Fabreguette

Multilayer and functional coatings on carbon nanotubes using atomic layer deposition

Atomic layer deposition (ALD) can be used to deposit ultra-thin and conformal films on flat substrates, high aspect ratios structures and particles. In this paper, we demonstrate that insulating, multilayered and functionalized ALD coatings can also be deposited conformally on carbon nanotubes. Multilayered coatings consisting of alternating layers of dielectric and conductive materials, such as Al2O3 and W, respectively, are deposited on conductive multi-walled carbon nanotubes. This coated carbon nanotube can function as a nanoscale coaxial cable. Thin layers of Al2O3 ALD are also used as a seed layer to functionalize nanotubes. A carbon nanotube was made highly hydrophobic using an Al2O3 ALD seed layer followed by the attachment of perfluorinated molecules.

Ultrahigh x-ray reflectivity from W∕Al2O3 multilayers fabricated using atomic layer deposition

W∕Al2O3 multilayers were fabricated using W and Al2O3 atomic layer deposition (ALD) to produce x-ray mirrors. The x-ray reflectivity from an optimized W∕Al2O3 multilayer was 96.5%±0.5% for the first-order Bragg peak at λ=1.54A. The ultrahigh x-ray reflectivity is attributed to the precise bilayer thicknesses and ultrasmooth interfaces obtained from ALD film growth. The self-limiting ALD surface chemistry prevents randomness during film growth and produces conformal deposition with correlated roughness that enhances the x-ray reflectivity.

Nucleation period, surface roughness, and oscillations in mass gain per cycle during W atomic layer deposition on Al2O3

Nucleation phenomena are critical for the fabrication of W/Al2O3 nanolaminates using atomic layer deposition (ALD) techniques. The nucleation and growth of W ALD on hydroxylated Al2O3 ALD surfaces and Al2O3 ALD on fluorinated W ALD surfaces was studied using in situ quartz crystal microbalance (QCM) and ex situ atomic force microscope (AFM) techniques. The QCM investigations revealed that Al2O3 ALD readily nucleated on the fluorinated W surface and displayed “substrate-enhanced growth.” In contrast, W ALD required 4–10 ALD cycles to nucleate on the hydroxylated Al2O3 surface and displayed “substrate-inhibited growth.” The W ALD nucleation period was shorter for higher Si2H6 and WF6 reactant exposures. The most rapid nucleation of W ALD on the Al2O3 surface occurred with much larger Si2H6 and WF6 exposures on the initial ALD cycle with the WF6 exposure prior to the Si2H6 exposure. By analyzing the individual Si2H6 and WF6 mass gain per cycle (MGPC), three main regions were identified in the W ALD nucleatio...

Multilayer coating method for x-ray reflectivity enhancement of polysilicon micro-mirrors at 1.54-Å wavelength

A poly-silicon piston micro-mirror array, which has been enhanced with a multilayer coating to exhibit special reflective properties at Cu Kα emission line of 1.54 Å is presented. The micro-mirror array is fabricated using the MEMSCAP PolyMUMPs process and packaged in a ceramic package. The packaged array is coated using atomic layer deposition with an Al2O3/W multilayer. The first Al2O3 layer is thicker than for a normal bilayer pair and prevents the mirror coating from creating an electrical short. This device was tested before and after coating. The snap-down voltage was reduced by half, but qualitatively the mechanical motion remained similar. The fabrication process presented for the Cu Kα wavelength at 1.54 Å can be easily adapted to other optical MEMS and for other wavelengths.