Synthesis Of Carbon Nitride Films At Low Temperatures

Carbon nitride films (CN x) have been deposited by sputtering a graphite target with nitrogen ions. Films were grown both with and without the presence of an assisting focused N 2 ion beam. The sputter beam voltage was varied between 150 and 1500 V and the applied assisting beam voltage from 80 to 500 V. The substrate was held at fixed temperatures between 80 and 673 K. The coatings were characterized with respect to their electrical, optical, and structural properties. The nitrogen content was measured by x-ray photoelectron spectroscopy (XPS) and a maximum nitrogen concentration of 44 at. % was obtained for a nonassisted sample deposited at 140 K. The chemical structure was investigated by XPS and Fourier transform infrared spectroscopy. Reduction of the substrate temperature in conjunction with low sputter beam voltages (<200 V) caused the optical band gap to increase up to 2.2 eV, the sheet conductivity to decrease to less th an 10 -9 (Ω cm) -1 and the density to be reduced to 1.6 g/cm 3. The increasing transparency is accompanied by structural changes indicating a transition from a predominantly sp 2 bonded amorphous sp 2/sp 3 C-N network to a more linear polymerlike structure consisting predominantly of doubly and triply bonded C and N atoms. No evidence for the formation of the β-C 3N 4 phase was found. © 1997 American Vacuum Society.151107112Hammer, P., Gissler, W., (1996) Diam. Relat. Mater., 5, p. 1152Hammer, P., Baker, M.A., Lenardi, C., Gissler, W., Thin Solid Films, , to be publishedTodorov, S.S., Marton, D., Boyd, K.J., Al-Bayati, A.H., Rabalais, J.W., (1994) J. Vac. Sci. Technol. A, 12, p. 3192Liu, A.Y., Cohen, M.L., (1990) Phys. Rev. B, 41, p. 10727Baker, M.A., Hammer, P., Surf. Interface Anal., , submittedKaufman, J.H., Metin, S., Saperstein, D.D., (1989) Phys. Rev. B, 39, p. 13053Dolphin, D., Wick, A., (1977) Tabulation of Infrared Spectral Data, , Wiley, New YorkSocrates, G., (1980) Infrared Characteristic Group Frequencies, , Wiley, Chichester, U.KSjöström, H., Stafström, S., Boman, M., Sundgren, J.E., (1995) Phys. Rev. Lett., 75, p. 1336Marton, D., Al-Bayati, A.H., Todorov, S.S., Boyd, K.J., Rabalais, J.W., (1994) Nucl. Instrum. Methods Phys. Res. B, 90, p. 277Sjöström, H., Hultman, L., Sundgren, J.-E., Hainsworth, S.V., Page, T.F., Theunissen, G.S.A.M., (1996) J. Vac. Sci. Technol. A, 14, p. 56Briggs, D., Clark, D.T., Keable, H.R., Kilner, M., (1973) J. Chem. Soc. Dalton Trans., p. 2143Barber, M., Conner, J.A., Guest, M.F., Hillier, I.H., Schwartz, M., Stacey, M., (1973) J. Chem. Soc. Faraday Trans. II, 69, p. 551Bircumshaw, L.L., Tayler, F.M., Whiffen, D.H., (1954) J. Chem. Soc., p. 93

Degradation of Image Quality Induced by Thermal Loads and Slope Errors in a XUV High Resolution Synchrotron Radiation Monochromator

The limiting effects to the performances of an optical device, such as an XUV monochromator inserted in a synchrotron radiation facility, are mainly manufacturing slope errors and thermal loads induced by the optical beam itself. We have performed numerical simulations on such effects in the low energy section of a high resolution, wide spectral range monochromator for the storage ring ELETTRA in Trieste. The instrument will be used in the dedicated surface physics beamline ALOISA (advanced line for overlayer interface and surface analysis). Thermal effects have been evaluated by using finite element analysis. Thermal induced deformations and slope errors have been included in a ray tracing program. The resulting aberrations at the output of the instrument have been evaluated for the extreme conditions of maximum power density and asymmetrical illumination of the second mirror. The results stress the relevance of manufacturing slope errors in limiting spatial and spectral resolution

Mechanotransduction in human and mouse beta cell lines: reliable models to characterize novel signaling pathways controlling beta cell fate

Background and aims: Attempts to influence \u3b2-cell differentiation by engineering substrates that mimic appropriate extracellular matrix (ECM) topographies are hampered by the fact that profound details of mechanosensing/transduction complexity remain elusive. We recently demonstrated that human islets of Langerhans sense the ECM nanotopography and activate a mechanotransductive pathway, which is essential for preserving long-term \u3b2-cell differentiation and function in vitro. However, human islets of Langerhans are extremely heterogeneous and their availability for research purpose is limited. Therefore, aim of the proposed research was to investigate whether mouse and human \u3b2-cell lines might sense changes innthe ECM topography and might be used as a simplified model to dissect the molecular pathways involved in mechanotransduction. Materials and methods: We used supersonic cluster beam deposition to fabricate nanostructured substrates characterized by a quantitatively controllable ECM-like nanoroughness. Mouse \u3b2TC3 and human 1.1B4 cells were seeded on these substrates and after five days in culture, the activation of the mechanotransductive pathway was verified by means of morphological (super-resolution fluorescence microscopy), functional and proteomic techniques. Results: Quantitative immunofluorescence studies demonstrated that the cell-nanotopography interaction affects the focal adhesion structures (smaller vinculin clusters), the organization of the actin cytoskeleton (shorter actin fiber) and the nuclear architecture. Functional studies revealed that nanostructured surfaces improve the \u3b2-cell mitochondrial activity and increase the glucose-stimulated Ca2+currents and insulin release. Label-free shotgun proteomics broadly confirmed the morphological and functional studies and showed the upregulation of a number of mechanosensors and transcription factors involved in \u3b2-cell differentiation in cells grown on nanostructured substrates compared to those grown on flat standard control surfaces. Conclusion: Our data reveal that mouse and human \u3b2-cell lines sense changes in extracellular mechanical forces and activate a mechanotransductive pathway. The findings from this study will be useful to clarify the link between mechanotransduction and cell fate and to successfully engineer scaffolds in order to have functional beta cells

Low-frequency modes in the Raman spectrum of sp-sp2 nanostructured carbon

A novel form of amorphous carbon with sp-sp2 hybridization has been recently produced by supersonic cluster beam deposition showing the presence in the film of both polyynic and cumulenic species [L. Ravagnan et al. Phys. Rev. Lett. 98, 216103 (2007)]. Here we present a in situ Raman characterization of the low frequency vibrational region (400-800 cm-1) of sp-sp2 films at different temperatures. We report the presence of two peaks at 450 cm-1 and 720 cm-1. The lower frequency peak shows an evolution with the variation of the sp content and it can be attributed, with the support of density functional theory (DFT) simulations, to bending modes of sp linear structures. The peak at 720 cm-1 does not vary with the sp content and it can be attributed to a feature in the vibrational density of states activated by the disorder of the sp2 phase.Comment: 15 pages, 5 figures, 1 tabl

The Effect of Mn Depleted Surface Layer on the Corrosion Resistance of Shape Memory Fe-Mn-Si-Cr Alloys

In this work, we have examined Fe-Mn-Si-Cr alloys possessing a good shape memory effect due to a high Mn content (28 wt pct). The addition of Cr (5 wt pct) was made in order to give fairly good corrosion resistance to the alloy. But we have verified that even in moderately corrosive environ-ments, the presence of chromium does not bear any passivation. On the other hand, we have found that the alloy can acquire corrosion resistance by means of the formation of a Mn-depleted surface layer obtained by heating the alloy at high temperature (.10507C) in air. This modified layer forms since manganese is selectively oxidized with respect to the other components. The adhesion of this layer is maintained even under severe stress if the thickness of the modified region does not exceed 20mm. Under this limit, the shape memory characteristics of the alloy are not affected, and at the same time, the specimen acquires properties of passivity comparable with one of the most common austenitic stainless steels at the presence of the same environmental conditions

Examination of thermally induced deformation of a synchrotron radiation mirror using finite element analysis

A synchrotron radiation mirror is subjected to high thermal loads that cause thermal gradients and surface distortions. The thermally induced deformations can strongly affect the transmission and the energy resolution of insertion device beamlines. We have performed heat transfer calculations and mechanical analyses in order to evaluate surface slope errors of a grazing\u2010incidence mirror. The parameters for these calculations have been chosen according to what will be a typical working situation at the synchrotron radiation facility of Trieste, presently under design. The analysis has been carried out by using the finite element method

Cellular response to cyclic compression of tissue engineered intervertebral disk constructs composed of electrospun polycaprolactone

There is lack of investigation capturing the complex mechanical interaction of tissue-engineered intervertebral disk (IVD) constructs in physiologically relevant environmental conditions. In this study, mechanical characterization of anisotropic electrospinning (ES) substrates made of polycaprolactone (PCL) was carried out in wet and dry conditions and viability of human bone marrow derived mesenchymal stem cells (hMSCs) seeded within double layers of ES PCL were also studied. Cyclic compression of IVD-like constructs composed of an agarose core confined by ES PCL double layers was implemented using a bioreactor and the cellular response to the mechanical stimulation was evaluated. Tensile tests showed decrease of elastic modulus of ES PCL as the angle of stretching increased, and at 60 deg stretching angle in wet, the maximum ultimate tensile strength (UTS) was observed. Based on the configuration of IVD-like constructs, the calculated circumferential stress experienced by the ES PCL double layers was 40 times of the vertical compressive stress. Confined compression of IVD-like constructs at 5% and 10% displacement dramatically reduced cell viability, particularly at 10%, although cell presence in small and isolated area can still be observed after mechanical conditioning. Hence, material mechanical properties of tissue-engineered scaffolds, composed of fibril structure of polymer with low melting point, are affected by the testing condition. Circumferential stress induced by axial compressive stimulation, conveyed to the ES PCL double layer wrapped around an agarose core, can affect the viability of cells seeded at the interface, depending on the mechanical configuration and magnitude of the load

Simulation of Berkovich nanoindentation experiments on thin films using finite element method

The Finite element technique is applied for studying the very complex stress-strain field of thin hard coatings subjected to a nanoindentation process. Berkovich indentation experiments were simulated with the ABAQUS finite element software package. The investigated system was titanium nitride on high speed steel as an example of a hard film on a softer substrate. The numerical analysis allowed the plastic deformation history during indentation to be followed. In particular, it was possible to correlate the onset of plastic deformation in the substrate with the shape of the loading curve. The system was simulated by an axisymmetric model in which the conical indenter has the same contact area as the Berkovich indenter. A six-fold symmetric three-dimensional model was also defined for testing the suitability of the previous model. The indenter was modeled either as a rigid surface or as a deformable diamond tip. Comparison between the experimental data and numerical results demonstrated that the finite element approach is capable of reproducing the loading-unloading behavior of a nanoindentation test. The film hardness of TiN/HSS specimens was numerically calculated for different indentation depths. It was shown that the presence of the substrate affected the hardness measurement for relative indentation depths greater than about 15% of the film thickness

Synthesis of carbon nitride films at low temperatures

Carbon nitride films (CNx) have been deposited by sputtering a graphite target with nitrogen ions. Films were grown both with and without the presence of an assisting focused N-2 ion beam. The sputter beam voltage was varied between 150 and 1500 V and the applied assisting beam voltage from 80 to 500 V. The substrate was held at fixed temperatures between 80 and 673 K. The coatings were characterized with respect to their electrical, optical; and structural properties. The nitrogen content was measured by x-ray photoelectron spectroscopy (XPS) and a maximum nitrogen concentration of 44 at. % was obtained for a nonassisted sample deposited at 140 K. The chemical structure was investigated by XPS and Fourier transform infrared spectroscopy. Reduction of the substrate temperature in conjunction with low sputter beam voltages (<200 V) caused the optical band gap to increase up to 2.2 eV, the sheet conductivity to decrease to less than 10(-9) (Omega cm)(-1) and the density to be reduced to 1.6 g/cm(3). The increasing transparency is accompanied by structural changes indicating a transition from a predominantly sp(2) bonded amorphous sp(2)/sp(3) C-N network to a more linear polymerlike structure consisting predominantly of doubly and triply bonded C and N atoms. No evidence for the formation of the beta-C3N4 phase was found

Proteomic Analysis Reveals a Mitochondrial Remodeling of &#946;TC3 Cells in Response to Nanotopography

Recently, using cluster-assembled zirconia substrates with tailored roughness produced by supersonic cluster beam deposition, we demonstrated that \u3b2 cells can sense nanoscale features of the substrate and can translate these stimuli into a mechanotransductive pathway capable of preserveing \u3b2-cell differentiation and function in vitro in long-term cultures of human islets. Using the same proteomic approach, we now focused on the mitochondrial fraction of \u3b2TC3 cells grown on the same zirconia substrates and characterized the morphological and proteomic modifications induced by the nanostructure. The results suggest that, in \u3b2TC3 cells, mitochondria are perturbed by the nanotopography and activate a program involving metabolism modification and modulation of their interplay with other organelles. Data were confirmed in INS1E, a different \u3b2-cell model. The change induced by the nanostructure can be pro-survival and prime mitochondria for a metabolic switch to match the new cell needs