Structural properties of silicon dioxide thin films densified by medium-energy particles

Classical molecular-dynamics simulations have been carried out to investigate densification mechanisms in silicon dioxide thin films deposited on an amorphous silica surface, according to a simplified ion-beam assisted deposition (IBAD) scenario. We compare the structures resulting from the deposition of near-thermal (1 eV) SiO$_{2}$ particles to those obtained with increasing fraction of 30 eV SiO$_{2}$ particles. Our results show that there is an energy interval - between 12 and 15 eV per condensing SiO$_2$ unit on average - for which the growth leads to a dense, low-stress amorphous structure, in satisfactory agreement with the results of low-energy ion-beam experiments. We also find that the crossover between low- and high-density films is associated with a tensile to compressive stress transition, and a simultaneous healing of structural defects of the {\em a-}SiO$_2$ network, namely three- and four-fold rings. It is observed, finally, that densification proceeds through significant changes at intermediate length scales (4--10 \AA), leaving essentially unchanged the ``building blocks'' of the network, viz. the Si(O$_{1/2}$)$_{4}$ tetrahedra. This latter result is in qualitative agreement with the mechanism proposed to explain the irreversible densification of amorphous silica recovered from high pressures ($\sim$ 15--20 GPa).Comment: 12 pages including 10 postscript figures; submitted to Phys. Rev. B; related publications can be found on web site http://www.centrcn.umontreal.ca/~lewi

VUV Photodeposition of Thiol-Terminated Films: A Wavelength-Dependent Study

Photoinitiated chemical vapor deposition (PICVD) has become attractive for selective and specific surface functionalization, because it relies on a single energy source, the photons, to carry out (photo-) chemistry. In the present wavelength (λ)-dependent study, thiol (SH)-terminated thin film deposits have been prepared from gas mixtures of acetylene (C2H2) and hydrogen sulfide (H2S) via PICVD using four different vacuum-ultraviolet (VUV) sources, namely, KrL (λpeak = 123.6 nm), XeL (λpeak = 147.0 nm), XeE (λpeak = 172.0 nm), and Hg (λ = 184.9 nm) lamps. Different λ influence the deposition kinetics and film composition, reflecting that photolytic reactions are governed by the gases’ absorption coefficients, k(λ). Thiol concentrations, [SH], up to ∼7.7%, were obtained with the XeL source, the highest reported in the literature so far. Furthermore, all films showed islandlike surface morphology, regardless of λ

Effect of nitrogen-rich cell culture surfaces on type X collagen expression by bovine growth plate chondrocytes

Background: Recent evidence indicates that osteoarthritis (OA) may be a systemic disease since mesenchymal stem cells (MSCs) from OA patients express type X collagen, a marker of late stage chondrocyte hypertrophy (associated with endochondral ossification). We recently showed that the expression of type X collagen was suppressed when MSCs from OA patients were cultured on nitrogen (N)-rich plasma polymer layers, which we call "PPE:N" (N-doped plasma-polymerized ethylene, containing up to 36 atomic percentage (at.%) of N.Methods: In the present study, we examined the expression of type X collagen in fetal bovine growth plate chondrocytes (containing hypertrophic chondrocytes) cultured on PPE:N. We also studied the effect of PPE: N on the expression of matrix molecules such as type II collagen and aggrecan, as well as on proteases (matrix metalloproteinase-13 (MMP-13) and molecules implicated in cell division (cyclin B2). Two other culture surfaces, "hydrophilic" polystyrene (PS, regular culture dishes) and nitrogen-containing cation polystyrene (Primaria (R)), were also investigated for comparison.Results: Results showed that type X collagen mRNA levels were suppressed when cultured for 4 days on PPE: N, suggesting that type X collagen is regulated similarly in hypertrophic chondrocytes and in human MSCs from OA patients. However, the levels of type X collagen mRNA almost returned to control value after 20 days in culture on these surfaces. Culture on the various surfaces had no significant effects on type II collagen, aggrecan, MMP-13, and cyclin B2 mRNA levels.Conclusion: Hypertrophy is diminished by culturing growth plate chondrocytes on nitrogen-rich surfaces, a mechanism that is beneficial for MSC chondrogenesis. Furthermore, one major advantage of such "intelligent surfaces" over recombinant growth factors for tissue engineering and cartilage repair is potentially large cost-saving

Energetics of reactions in an atmospheric pressure plasma jet with argon carrier gas and hexamethyldisiloxane reagent

ABSTRACT: We report on a methodology for measuring the energy dissipated per AC high voltage cycle in a cold atmospheric pressure plasma jet (CAPJet). This method is adapted from research by Nisol et al. on plasma polymerization of hexamethyldisiloxane (HMDSO) organosilicon vapor in a large area planar dielectric barrier discharge (DBD) reactor. Here too, we measured ΔEg, the energy difference with and without small HMDSO vapor concentrations in the argon carrier gas flow. From ΔEg we then derived Em, the energy per molecule, and compared values with those of Nisol. Good agreements were found, including in film structures determined from attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectra, thus suggesting that realistic Em values can be successfully obtained also for the CAPJet case

Sulfur-rich organic films deposited by plasma- and vacuum-ultraviolet (VUV) photo-polymerization

Thiol (SH)-terminated surfaces have been progressively gaining interest over the past years as a consequence of their widespread potential applications. Here, SH-terminated thin films have been prepared by “co-polymerizing” gas mixtures comprising ethylene (C2H4) or butadiene (C4H6) with hydrogen sulfide (H2S). This has been accomplished by either vacuum-ultraviolet (VUV) irradiation of the flowing gas mixtures with near-monochromatic radiation from a Kr lamp, or by low-pressure r.f. plasma-enhanced chemical vapor deposition (PECVD). Varying the gas mixture ratio, R, allows one to control the films’ sulfur content as well as the thiol concentration [[BOND]SH]. The deposits were characterized by X-ray photoelectron spectroscopy (XPS), before and after chemical derivatization with N-ethylmaleimide, and by ATR FTIR. VUV- and plasma-prepared coatings were found to possess very similar structures and characteristics, showing chemically bonded sulfur concentrations, [S], up to 48 at% and [[BOND]SH] up to 3%. All coatings remained essentially unchanged in thickness after immersion in water for 24 h

Epidemiology of eating disorders part III: Social epidemiology and case definitions revisited.

Accepted manuscript version. Published version at <a href=http://doi.org/10.1080/21662630.2015.1022197>http://doi.org/10.1080/21662630.2015.1022197</a>.The previous papers in this series outlined a historical panorama and presented updated knowledge about putative risk factors and how eating disorders are distributed in various populations. In this final paper, we discuss in what way comorbidity findings and transdiagnostic issues may change our conceptions about ‘an epidemiological case’ from the current definition of eating disorders based on the recent version of the Diagnostic and Statistical Manual of Mental Disorders (i.e. the DSM-5), and to what extent an alternative definition may introduce new perspectives of prevention. The paper also provides an update on issues relevant for treatment dissemination

Growth mechanisms of sulfur-rich plasma polymers: Binary gas mixtures versus single precursor

Thiol (SH)‐terminated surfaces have gained interest over the past years due to their potential applications, especially in the biomedical field. In this work, SH‐terminated films have been prepared by “co‐polymerizing” gas mixtures of acetylene (C2H2) and hydrogen sulfide (H2S) using low‐pressure r.f. plasma‐enhanced chemical vapor deposition. R.f. power greatly influences the deposition rate, sulfur content, [S], and thiol concentration, [SH], of the films, as confirmed by XPS (both before and after chemical derivatization), FTIR, and mass spectrometry measurements. These data are compared with those obtained in a similar discharge by using a single molecule precursor, propanethiol. Among other differences, it is demonstrated that [SH] is higher when using binary gas mixtures compared to the single molecule precursor

Organic coatings from acetylene at atmospheric pressure: UV light versus plasma

ABSTRACT: A versatile pilot-scale reactor has been designed in such a way that it can be readily converted from a dielectric barrier discharge “PECVD” operating mode into a photoinitiated “PICVD” one; in the latter, low-pressure mercury (Hg) lamps replace the high-voltage glow discharge plasma. Both processes operate at ambient temperature and atmospheric pressure, 100 kPa, using acetylene (C2H2) monomer. In both sets of experiments, it was found that efficient gas-to-solid conversion can occur in the form of a nanoparticulate amorphous hydrocarbon polymer-like material. It was found that in the PICVD case, great care was required to exclude even traces of O2 contamination, because it not only reduced the growth rate of solid, but the latter then became highly oxidized ([O] ~50 at.%) and water-soluble