Physical and optical properties of the International Simple Glass

Radioactive waste immobilization is a means to limit the release of radionuclides from various waste streams into the environment over a timescale of hundreds to many thousands of years. Incorporation of radionuclide-containing wastes into borosilicate glass during vitrification is one potential route to accomplish such immobilization. To facilitate comparisons and assessments of reproducibility across experiments and laboratories, a six-component borosilicate glass (Si, B, Na, Al, Ca, Zr) known as the International Simple Glass (ISG) was developed by international consensus as a compromise between simplicity and similarity to waste glasses. Focusing on a single glass composition with a multi-pronged approach utilizing state-of-the-art, multi-scale experimental and theoretical tools provides a common database that can be used to assess relative importance of mechanisms and models. Here we present physical property data (both published and previously unpublished) on a single batch of ISG, which was cast into individual ingots that were distributed to the collaborators. Properties from the atomic scale to the macroscale, including composition and elemental impurities, phase purity, density, thermal properties, mechanical properties, optical and vibrational properties, and the results of molecular dynamics simulations are presented. In addition, information on the surface composition and morphology after polishing is included. Although the existing literature on the alteration of ISG is not extensively reviewed here, the results of well-controlled static alteration experiments are presented here as a point of reference for other performance investigations

Molecular modeling of alkyl monolayers on the Si (100)-2 x 1 surface

Molecular modeling was used to simulate various surfaces derived from the addition of 1-alkenes and 1-alkynes to Si=Si dimers on the Si(100)-2 × 1 surface. The primary aim was to better understand the interactions between adsorbates on the surface and distortions of the underlying silicon crystal due to functionalization. Random addition of ethylene and acetylene was used to determine how the addition of an adduct molecule affects subsequent additions for coverages up to one molecule per silicon dimer, that is, 100% coverage. Randomization subdues the effect that the relative positions of the adsorbates have on the enthalpy of the system. For ethylene and acetylene, the enthalpy of reaction changes less than 3 and 5 kcal/mol, respectively, from the first reacted species up to 100% coverage. As a result, a (near-)complete coverage is predicted, which is in line with experimental data. When 1-alkenes and 1-alkynes add by [2 + 2] addition, the hydrocarbon chains interact differently depending on the direction they project from the surface. These effects were investigated for four-carbon chains: 1-butene and 1-butyne. As expected, the chains that would otherwise intersect bend to avoid each other, raising the enthalpy of the system. For alkyl chains longer than four carbons, the chains are able to reorient themselves in a favorable manner, thus, resulting in a steady reduction in reaction enthalpy of about 2 kcal/mol for each additional methylene unit

Covalent biofunctionalization of silicon nitride surfaces

Covalently attached organic monolayers on etched silicon nitride (SixN4; x 3) surfaces were prepared by reaction of SixN4-coated wafers with neat or solutions of 1-alkenes and 1-alkynes in refluxing mesitylene. The surface modification was monitored by measurement of the static water contact angle, XPS, IRRAS, AFM, and ToF-SIMS, and evidence for the formation of Si-C bonds is presented. The etching can be achieved by dilute HF solutions and yields both Si-H and N-H moieties. The resulting etched SixN4 surfaces are functionalized by terminal carboxylic acid groups in either of two ways: (a) via attachment of a 10-undecenoic acid 2,2,2-trifluoroethyl ester (trifluoro ethanol ester) and subsequent thermal acid hydrolysis; (b) through attachment of a photocleavable ester, and subsequent photochemical cleavage, as this would allow photopatterned functionalized SixN4. The carboxylic acids are successfully used for the attachment of oligopeptides (aspartame) and complete proteins using EDC/NHS chemistry. Finally, an amino-terminated organic monolayer can be formed by reaction of HF-treated SixN4 surfaces with a N-(-undecylenyl)phthalimide, which yields an amino-terminated surface upon deprotection with hydrazine