Stable organic monolayers on oxide-free silicon/germanium in a supercritical medium: A new route to molecular electronics

10.1021/jz4005416Journal of Physical Chemistry Letters491397-140

Deposition of zwitterionic polymer brushes in a dense gas medium

Poly(sulfobetaine methacrylate) (PSBMA) films known for their resistance to nonspecific protein adsorption, cell/bacterial adhesion and biofilm formation were produced by surface initiated polymerization on a silicon surface via a batch reaction system in CO2 expanded liquid (CO2-EL) medium. Atom transfer radical polymerization (ATRP) was carried out using 2,2′-bipyridyl as ligand and CuBr as a catalyst in water/methanol mixture with trichloro[4-(chloromethyl)phenyl]silane (CMPS) used as the initiating species. The films were grown in the CO2-EL environment at a range of conditions and thickness up to 10 nm. In contrast to films produced by conventional solvent systems at atmospheric pressure, the polymer films grown by the CO2-EL process showed uniform thickness and pin-hole free topography. Most importantly, the CO2-EL processed PSBMA films showed no trace of copper (used as the catalyst), thus obviating the need for post-deposition processing and avoiding adverse effects of the metal leaching during service. Finally, PSBMA films from both the conventional and CO2-EL processes were exposed to Human mesenchymal stem cells (hMSCs) and the results showed that, while in both the cases the cell proliferation rate was inhibited by the charged polymeric brush surface, the CO2-EL-processed brush exhibited inhibition to a larger extent due to the reduced occurrence of pinholes. The process can be easily exploited effectively when carrying out surface initiated polymerization on non-flat topographies, such as in trenches and nanostructured features with high aspect ratios

Molecular Electronics at Metal/Semiconductor Junctions. Si Inversion by Sub-Nanometer Molecular Films

Electronic transport across n-Si-alkyl monolayer/Hg junctions is, at reverse and low forward bias, independent of alkyl chain length from 18 down to 1 or 2 carbons! This and further recent results indicate that electron transport is minority, rather than majority carrier dominated, occurs via generation and recombination, rather than (the earlier assumed) thermionic emission, and, as such, is rather insensitive to interface properties. The (m)ethyl results show that binding organic molecules directly to semiconductors provides semiconductor/metal interface control options, not accessible otherwise

Dynamic and static characteristics of drug dissolution in supercritical CO2 by infrared spectroscopy : measurements of acetaminophen solubility in a wide range of state parameters

In this work we use infrared spectroscopy to investigate solubility properties of a bioactive substance in supercritical CO2 (scCO2). By using acetaminophen as a model compound, we show that the method can provide high sensitivity that makes it possible to study solubility at small concentrations, up to 10-6 mol·L-1. This method also allows one to investigate the kinetics of the dissolution process in supercritical solvent. Our measurements at two different points of the (p, T) plane ((40 MPa, 373 K) and (40 MPa, 473 K)) have shown significant difference in the kinetic mechanisms of acetaminophen dissolution at these two states: at higher temperature the dissolution process in scCO2 has two steps: (i) "fast" step when the acetaminophen concentration in scCO2 quickly reaches (70 to 80) % of the saturation level and (ii) a subsequent "slow" step where the acetaminophen concentration slowly increases up to the saturation level. However, at lower temperature, the dissolution process has only one, "slow" step