Carbon‐Enriched Amorphous Hydrogenated Boron Carbide Films for Very‐Low‐k Interlayer Dielectrics

A longstanding challenge in ultralarge‐scale integration has been the continued improvement in low‐dielectric‐constant (low‐k) interlayer dielectric materials and other specialized layers in back‐end‐of‐the‐line interconnect fabrication. Modeled after the success of carbon‐containing organosilicate materials, carbon‐enriched amorphous hydrogenated boron carbide (a‐BxC:Hy) films are grown by plasma‐enhanced chemical vapor deposition from ortho‐carborane and methane. These films contain more extraicosahedral sp3 hydrocarbon groups than nonenriched a‐BxC:Hy films, as revealed by FTIR and NMR spectroscopy, and also exhibit lower dielectric constants than their nonenriched counterparts, notably due to low densities combined with a low distortion and orientation contribution to the total polarizability. Films with dielectric constant as low as 2.5 are reported with excellent electrical stability (leakage current of 10−9 A cm−2 at 2 MV cm−1 and breakdown voltage of >6 MV cm−1), good thermal conductivity of 0.31 ± 0.03 W m−1 K−1, and high projected Young’s modulus of 12 ± 3 GPa. These properties rival those of leading SiOC:H materials, and position a‐BxC:Hy as an important complement to traditional Si‐based materials to meet the complex needs of next‐generation interconnect fabrication.Carbon‐enriched amorphous hydrogenated boron carbide films are demonstrated with dielectric constant (k) as low as 2.5—attributed to low densities combined with network‐rigidifying CH2 bridging groups—as well as excellent electrical, thermal, and mechanical properties, rivaling those of state‐of‐the‐art silicon‐based low‐k dielectric materials.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141869/1/aelm201700116_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141869/2/aelm201700116.pd

Spectroscopic analysis of interactions between alkylated silanes and alumina nanoporous membranes

Transport across alumina nanoporous membranes can be altered via surface attachment of alkylated trimethoxysilane compounds. The mechanism of attachment has been previously assumed to be monolayer silane coverage through full chemisorption regardless of reaction conditions. This chemisorption arises via covalent Si–O–Al bond formation resulting from condensation between the three putative silanols (due to hydrolysis of the three Si–OCH3 bonds) and hydroxides present on the alumina surface. If this model was correct, methanol would be produced in large quantities in the reaction solution, and the methoxy moieties would no longer be present on the silane molecule. The results presented in this paper utilized FT-IR and both solution and solid-state NMR to examine the chemical nature of octadecyltrimethoxysilane (ODTMS) present on the alumina surface. The FT-IR results confirm the presence of the silane on the membrane. The 1H solution NMR results indicate small but detectable methanol production during attachment. The solid-state NMR results demonstrate that the methoxy proton NMR integrated peak intensities remain in nearly the same ratios present in the free silane, concluding that the majority of methoxy groups are intact while the silane is attached to the membrane surface. These three results suggest that monolayer surface coverage and chemisorption through full covalent bonding is not the primary means of attachment for ODTMS on the surface of alumina nanomembranes under these reaction conditions

Supramolecular Structure in Full-Length Alzheimer's β-Amyloid Fibrils: Evidence for a Parallel β-Sheet Organization from Solid-State Nuclear Magnetic Resonance

We report constraints on the supramolecular structure of amyloid fibrils formed by the 40-residue β-amyloid peptide associated with Alzheimer's disease (Aβ1–40) obtained from solid-state nuclear magnetic resonance (NMR) measurements of intermolecular dipole-dipole couplings between 13C labels at 11 carbon sites in residues 2 through 39. The measurements are carried out under magic-angle spinning conditions, using the constant-time finite-pulse radiofrequency-driven recoupling (fpRFDR-CT) technique. We also present one-dimensional 13C magic-angle spinning NMR spectra of the labeled Aβ1–40 samples. The fpRFDR-CT data reveal nearest-neighbor intermolecular distances of 4.8 ± 0.5 Å for carbon sites from residues 12 through 39, indicating a parallel alignment of neighboring peptide chains in the predominantly β-sheet structure of the amyloid fibrils. The one-dimensional NMR spectra indicate structural order at these sites. The fpRFDR-CT data and NMR spectra also indicate structural disorder in the N-terminal segment of Aβ1–40, including the first nine residues. These results place strong constraints on any molecular-level structural model for full-length β-amyloid fibrils.Validerad; 2002; 20070417 (bajo)</p

Tenofovir Containing Thiolated Chitosan Core/Shell Nanofibers: <i>In Vitro</i> and <i>in Vivo</i> Evaluations

It is hypothesized that thiolated chitosan (TCS) core/shell nanofibers (NFs) can enhance the drug loading of tenofovir, a model low molecular weight and highly water-soluble drug molecule, and improve its mucoadhesivity and <i>in vivo</i> safety. To test this hypothesis, poly­(ethylene oxide) (PEO) core with TCS and polylactic acid (PLA) shell NFs are fabricated by a coaxial electrospinning technique. The morphology, drug loading, drug release profiles, cytotoxicity and mucoadhesion of the NFs are analyzed using scanning and transmission electron microscopies, liquid chromatography, cytotoxicity assays on VK2/E6E7 and End1/E6E7 cell lines and <i>Lactobacilli crispatus</i>, fluorescence imaging and periodic acid colorimetric method, respectively. <i>In vivo</i> safety studies are performed in C57BL/6 mice followed by H&E and immunohistochemical (CD45) staining analysis of genital tract. The mean diameters of PEO, PEO/TCS, and PEO/TCS-PLA NFs are 118.56, 9.95, and 99.53 nm, respectively. The NFs exhibit smooth surface. The drug loading (13%–25%, w/w) increased by 10-fold compared to a nanoparticle formulation due to the application of the electrospinning technique. The NFs are noncytotoxic at the concentration of 1 mg/mL. The PEO/TCS-PLA core/shell NFs mostly exhibit a release kinetic following Weibull model (<i>r</i>² = 0.9914), indicating the drug release from a matrix system. The core/shell NFs are 40–60-fold more bioadhesive than the pure PEO based NFs. The NFs are nontoxic and noninflammatory <i>in vivo</i> after daily treatment for up to 7 days. Owing to their enhanced drug loading and preliminary safety profile, the TCS core/shell NFs are promising candidates for the topical delivery of HIV/AIDS microbicides such as tenofovir