The global warming intensities of crop-based biofuels and fossil fuels differ not only in amount but also in their discharge patterns over time. Early discharges, for example, from market-mediated land use change, will have created more global warming by any time in the future than later discharges, owing to the slow decay of atmospheric CO 2 . A spreadsheet model of this process, BTIME, captures this important time pattern effect using the Bern CO 2 decay model to allow fuels to be compared for policy decisions on the basis of their real warming effects with a variety of user-supplied parameter values. The model also allows economic discounting of climate effects extended far into the future. Compared to approaches that simply sum greenhouse gas emissions over time, recognizing the physics of atmospheric CO 2 decay significantly increases the deficit relative to fossil fuel of any biofuel causing land use change.

Special k: Pure silica zeolites (PSZs) have been shown experimentally to display a remarkably higher elastic modulus than amorphous porous silicas at any given porosity or dielectric constant (k) value as a result of their crystalline structure. The combined experimental and theoretical findings suggest that PSZs have the necessary properties for use as the next generation of low‐k insulators.

We study the interaction between two parallel surfaces having a polymertethered ligand on one and a random distribution of receptors on the other. We examine the interplay between the specific ligand-receptor binding and the conformation degrees of freedom of the polymer tether, and address the difference between the cases of mobile (annealed) and immobile (quenched) receptors. The annealed case is solved exactly and the quenched case is treated by both Monte Carlo direct sampling and an analytical density expansion. The combination of the entropic repulsion due to chain confinement at small surface separations, and the attraction due to ligand-receptor binding which can take place at significant chain stretching, results in a minimum in the interaction free energy. For the same set of parameters, stronger binding is obtained for the annealed case than for the quenched case, reflecting the ability of the mobile receptors to migrate into the region of the ligand. In the quenched case, binding is limited by the availability of receptors within the reach of the ligand; for a given receptor density and binding energy, there exists an optimal chain length that yields the lowest minimum in the interaction free energy for the quenched case.

k wie konkurrenzlos: Wegen ihrer kristallinen Struktur zeigten Zeolithe aus reinem Siliciumdioxid (pure silica zeolites, PSZs) in Experimenten bei jeder betrachteten Porosität oder Dielektrizitätskonstante (k) deutlich höhere Elastizitätsmoduln als amorphes Siliciumdioxid. Experimentelle und theoretische Ergebnisse deuten an, dass PSZs als nächste Generation von Low‐k‐Isolatoren infrage kommen.

Most organosilicate glass 1 (OSG), low dielectric constant (low-) films contain Si-R groups, where R is an organic moiety such as -CH 3 . The organic component is susceptible to the chemically reactive plasmas used to deposit cap layers, etch patterns, and ash photoresist. This study compares a spin-on, mesoporous OSG film with a completely connected pore structure to both its nonmesoporous counterpart and to another low-density OSG film deposited by plasma-enhanced chemical vapor deposition. The results show that the film with connected pores was much more susceptible to integration damage than were the nonmesoporous OSG films.As integrated circuit device and interconnect dimensions continue to scale smaller, low dielectric constant () interlayer dielectric (ILD) materials will become necessary to mitigate RC (product of resistance and capacitance) propagation delay and reduce power consumption and crosstalk. 1 Lowering the -value of a material requires either altering the chemical bonding to reduce the bond polarizability or decreasing the number of bonds (density) in a material. 2 To reduce the -value below 2.2, most dielectric materials will require a density decrease by introducing free volume (micropores < 2 nm in diameter) or mesoporosity (2-50 nm diameter pores). Unfortunately, lowering the density also compromises the mechanical strength and other properties of the material. 2 The material properties of mesoporous dielectric films, such as connected pores and low mechanical strength, create a host of integration problems including integration damage to the film. 3,4 The Si-R groups make organosilicate glass (OSG) films hydrophobic and they lower the density by breaking up the tetrahedral Si-O bonding. However, the carbon component is susceptibleto degradation when exposed to the reactive plasmas used for capping, etching, and ashing processes, especially oxidizing plasmas that induce silanol formation. Such plasma-induced chemical modifications can cause film densification, dangling bonds and defects, and moisture uptake. 5,6 Recently, International SEMATECH monitored several OSG films for change in caused by integration damage (ID) while integrating the films into SEMATECH's Cu/Damascene test chip using their standard processing flow (Table I). 7 Mesoporous OSG films with connected pores exhibited a large increase in due to ID during integration. In contrast, nonmesoporous OSG films showed much smaller changes in . Thus, connected mesoporosity appears to facilitate film damage during processing by allowing reactive species to more easily penetrate the film.Various plasma pretreatments (PPT) have been reported to form densified and chemically modified interface layers on OSG films, and these skin layers can prevent film damage by photoresist ash processes. [8][9][10] This study reports the effects of oxygen and nitrogenbased plasmas on one mesoporous and two nonmesoporous blanket films. To our knowledge, this is the first direct demonstration that a mesoporous film is more susceptible to ID than its nonm...