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1.  Facile Pyrolytic Synthesis of Silicon Nanowires 
Solid-state electronics  2010;54(10):1185-1191.
One-dimensional nanostructures such as silicon nanowires (SiNW) are attractive candidates for low power density electronic and optoelectronic devices including sensors. A new simple method for SiNW bulk synthesis[1, 2] is demonstrated in this work, which is inexpensive and uses low toxicity materials, thereby offering a safe, energy efficient and green approach. The method uses low flammability liquid phenylsilanes, offering a safer avenue for SiNW growth compared with using silane gas. A novel, duo-chamber glass vessel is used to create a low-pressure environment where SiNWs are grown through vapor-liquid-solid mechanism using gold nanoparticles as a catalyst. The catalyst decomposes silicon precursor vapors of diphenylsilane and triphenylsilane and precipitates single crystal SiNWs, which appear to grow parallel to the substrate surface. This opens up possibilities for synthesizing nano-junctions amongst wires which is important for the grid architecture of nanoelectronics proposed by Likharev[3]. Even bulk synthesis of SiNW is feasible using sacrificial substrates such as CaCO3 that can be dissolved post-synthesis. Furthermore, by dissolving appropriate dopants in liquid diphenylsilane, a controlled doping of the nanowires is realized without the use of toxic gases and expensive mass flow controllers. Upon boron doping, we observe a characteristic red shift in photoluminescence spectra. In summary, an inexpensive and versatile method for SiNW is presented that makes these exotic materials available to any lab at low cost.
PMCID: PMC2919782  PMID: 20711489
Silicon nanowires; dopants; photoluminescence; gold nanoparticles; HR-TEM
2.  Differential Effects of the Hydrophobic Surfactant Proteins on the Formation of Inverse Bicontinuous Cubic Phases 
Prior studies have shown that the biological mixture of the two hydrophobic surfactant proteins, SP–B and SP–C, produces faster adsorption of the surfactant lipids to an air/water interface, and that they induce 1-palmitoyl-2-oleoyl phosphatidylethanolamine (POPE) to form inverse bicontinuous cubic phases. Previous studies have shown that SP–B has a much greater effect than SP–C on adsorption. If the two proteins induce faster adsorption and formation of the bicontinuous structures by similar mechanisms, then they should also have different abilities to form the cubic phases. To test this hypothesis, we measured small angle X-ray scattering on the individual proteins combined with POPE. SP–B replicated the dose-related ability of the combined proteins to induce the cubic phases at temperatures more than 25°C below the point at which POPE alone forms the curved inverse-hexagonal phase. With SP–C, diffraction from cubic structures was either absent or present at very low intensities only with larger amounts of protein. The correlation between the structural effects of inducing curved structures and the functional effects on the rate of adsorption fits with the model in which SP–B promotes adsorption by facilitating formation of an inversely curved, rate-limiting structure.
PMCID: PMC3514604  PMID: 23140329
adsorption; bending; curvature; lipid polymorphisms; lung; pulmonary surfactant
3.  Effects of gramicidin-A on the adsorption of phospholipids to the air–water interface 
Biochimica et biophysica acta  2005;1717(1):41-49.
Prior studies suggest that the hydrophobic surfactant proteins, SP-B and SP-C, promote adsorption of the lipids in pulmonary surfactant to an air–water interface by stabilizing a negatively curved rate-limiting structure that is intermediate between bilayer vesicles and the surface film. This model predicts that other peptides capable of stabilizing negative curvature should also promote lipid adsorption. Previous reports have shown that under appropriate conditions, gramicidin-A (GrA) induces dioleoyl phosphatidylcholine (DOPC), but not dimyristoyl phosphatidylcholine (DMPC), to form the negatively curved hexagonal-II (HII) phase. The studies reported here determined if GrA would produce the same effects on adsorption of DMPC and DOPC that the hydrophobic surfactant proteins have on the surfactant lipids. Small angle X-ray scattering and 31P-nuclear magnetic resonance confirmed that at the particular conditions used to study adsorption, GrA induced DOPC to form the HII phase, but DMPC remained lamellar. Measurements of surface tension showed that GrA in vesicles produced a general increase in the rate of adsorption for both phospholipids. When restricted to the interface, however, in preexisting films, GrA with DOPC, but not with DMPC, replicated the ability of the surfactant proteins to promote adsorption of vesicles containing only the lipids. The correlation between the structural and functional effects of GrA with the two phospholipids, and the similar effects on adsorption of GrA with DOPC and the hydrophobic surfactant proteins with the surfactant lipids fit with the model in which SP-B and SP-C facilitate adsorption by stabilizing a rate-limiting intermediate with negative curvature.
PMCID: PMC3490622  PMID: 16242116
Gramicidin; Lipid polymorphism; 31P nuclear magnetic resonance; Pulmonary surfactant; Hydrophobic surfactant protein; Small angle x-ray scattering
4.  The Accelerated Late Adsorption of Pulmonary Surfactant 
Langmuir  2011;27(8):4857-4866.
Adsorption of pulmonary surfactant to an air−water interface lowers surface tension (γ) at rates that initially decrease progressively, but which then accelerate close to the equilibrium γ. The studies here tested a series of hypotheses concerning mechanisms that might cause the late accelerated drop in γ. Experiments used captive bubbles and a Wilhelmy plate to measure γ during adsorption of vesicles containing constituents from extracted calf surfactant. The faster fall in γ reflects faster adsorption rather than any feature of the equation of state that relates γ to surface concentration (Γ). Adsorption accelerates when γ reaches a critical value rather than after an interval required to reach that γ. The hydrophobic surfactant proteins (SPs) represent key constituents, both for reaching the γ at which the acceleration occurs and for producing the acceleration itself. The γ at which rates of adsorption increase, however, is unaffected by the Γ of protein in the films. In the absence of the proteins, a phosphatidylethanolamine, which, like the SPs, induces fusion of the vesicles with the interfacial film, also causes adsorption to accelerate. Our results suggest that the late acceleration is characteristic of adsorption by fusion of vesicles with the nascent film, which proceeds more favorably when the Γ of the lipids exceeds a critical value.
PMCID: PMC3074574  PMID: 21417351

Results 1-4 (4)