Preparation of tetrahedral amorphous carbon films by filtered cathodic vacuum arc deposition

Tetrahedrally bonded amorphous carbon (ta-C) and nitrogen doped (ta-C:N) films were obtained at room temperature in a filtered cathodic vacuum arc (FCVA) system incorporating an off-plane double bend (S-bend) magnetic filter. The influence of the negative bias voltage applied to substrates (from -20 to -350 V) and the nitrogen background pressure (up to 10-3 Torr) on film properties was studied by scanning electron microscopy (SEM), electron energy loss spectroscopy (EELS), Raman spectroscopy, X-ray photoemission spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and X-ray reflectivity (XRR). The ta-C films showed sp3 fractions between 84% and 88%, and mass densities around 3.2 g/cm3 in the wide range of bias voltage studied. In contrast, the compressive stress showed a maximum value of 11 GPa for bias voltages around -90 V, whereas for lower and higher bias voltages the stress decreased to 6 GPa. As for the ta-C:N films grown at bias voltages below -200 V and with N contents up to 7%, it has been found that the N atoms were preferentially sp3 bonded to the carbon network with a reduction in stress below 8 GPa. Further increase in bias voltage or N content increased the sp2 fraction, leading to a reduction in film density to 2.7 g/cm3.

Studies on radiation pasteurisation of medium fatty fish 1. Control of radiation induced oxidative changes in white pomfret (Stromateus cinereus) by vacuum packaging

Marked differences were observed in proximate biochemical compositions of the skin and muscle of white pomfret. The skin showed comparatively higher content of extractable lipids and was more susceptible to radiation-induced oxidative changes like development of rancid odours and yellow discolouration than the muscle. Irradiation of skin samples under vacuum suppressed these changes. The present paper also reports on the efficacy of vacuum packaging in controlling oxidative rancidity and yellow discolouration in white pomfret skin subjected to irradiation and subsequent storage at 0-2°C.

Application of combined effect of sodium acetate and nisin on reduction of contamination by Listeria monocytogenes in vacuum packaged grass carp (Ctenopharyngodon idella) fillets kept at 4°C

In this study microbiological , chemical quality and fatty acid composition of grass carp (Ctenopharyngodon idella) fillets treated by dipping in sodium acetate (%1 and %3), nisin (% 0.1 and % 0.2) and combination of sodium acetate and nisin was evaluated during 16 days of refrigerated of 4°C Antilisterial effect of nisin was enhanced with the increased concentration of sodium acetate. At day 12 post storage, Listeria monocytogenese count was higher in the control group than the recommended value, however in sodium acetate and nisin treated samples, the count was lower (5.17-5.91 log cfu/g). With increasing the concentrations of sodium acetate, mesophilic counts were lower. Regarding nisin, better results was obtained by applying %0.1 nisin. Greater inhibition of mesophile bacteria was observed when combination treatment was used. The number of lactobacillus was lower when higher concentrations of sodium acetate and nisin were used. Total Volatile Nitrogen values at the end of the experiment were lower in the samples treated with both nisin and sodium acetate and the better results were obtained in combination treatments. Peroxide (PV) at the end of the experiment was 1.9 meq/kg in control, and the lowest values were observed for the treatments 3(%0 sodium acetate +% 0.2 nisin) and 9(%3 sodium acetate +% 0.2 nisin) between 1.08 and 1.62 meq/kg without significant difference. Thiobarbituric acid (TBA) levels at the end of experiment have been shown to be 0.46 mg malonaldehyde per kg in the control. On the other hand treatments 9 had the TBA values of 0.19 mg malonaldehyde per kg which was significantly lower than that of control. Polyunsaturated fatty acids increased by increasing the sodium acetate doses and instead saturated fatty acids and n-6/n-3 ratio decreased. The ratio of UFA/SFA and also C22:6/C16:0 increased when a higher concentration of sodium acetate has been used. The best result obtained by using 3% of sodium acetate but no such relation with nisin was observed.

Study on the sustainability of FPC produced from Kilka (Clupeonella engrauliformis, C. grimmi and C. cultriventris) in two vacuum packaging and modified atmosphere packaging at different environmental factors

Fish protein concentrate (FPC) is a healthy, sustainable and high nutritive product which sanitized produced from fishes in which, protein and other nutrients are more concentrated than in fresh fishes. The aim of this research is to study on the sustainability of FPC produced from Kilka (Clupeonella engrauliformis , C. grimmi and C. cultriventris) in two Vaccum Packaging and Modified Atmosphere Packaging at different environmental factors during six months. In our study the analysis of FPC protein showed 91.2%, lipid: 0.5%, ash: 3.6%, moisture: 2.3%, Total Volatile Nitrogen: 10 ml/100gr and peroxide: 5meq/kg. Amino acids and fatty acids were also determined. Bacteria and Fungi were lower than 1000 colony. Samples are kept in different condition of temperature (5, 20 and 35 degree centigrade), humidity (25, 40 and 90 percent) and light and dark environment in six month. Lipid rate in FPC after 6 months in VP and MAP (60% C02, 30 % N2 and 10% O2), packages was decreased but was not significant (P>0.05). It was also detected that increase temperature lead to more decrease in lipid content. Protein rate of FPC was decreased from 91.2% to 73.6% during six months at 35°C in VP Package and from 91.2% to 69.4% in MAP package. These changes were significant (P<0.05). TVN and PV rate in FPC after 6 months in VP and MAP packages was increased but was significant (P<0.05). Amino acids and fatty acids were also determined. But more changes in MAP packages was detected.

Properties of tetrahedral amorphous carbon prepared by vacuum arc deposition

The structural, optical, electrical and physical properties of amorphous carbon deposited from the filtered plasma stream of a vacuum arc were investigated. The structure was determined by electron diffraction, neutron diffraction and energy loss spectroscopy and the tetrahedral coordination of the material was confirmed. The measurements gave a nearest neighbour distance of 1.53 Å, a bond angle of 110 and a coordination number of four. A model is proposed in which the compressive stress generated in the film by energetic ion impact produces pressure and temperature conditions lying well inside the region of the carbon phase diagram within which diamond is stable. The model is confirmed by measurements of stress and plasmon energy as a function of ion energy. The model also predicts the formation of sp2-rich materials on the surface owing to stress relaxation and this is confirmed by a study of the surface plasmon energy. Some nuclear magnetic resonance, infrared and optical properties are reported and the behaviour of diodes using tetrahedral amorphous carbon is discussed. © 1991.

Increasing the open-circuit voltage of photoprotein-based photoelectrochemical cells by manipulation of the vacuum potential of the electrolytes.

The innately highly efficient light-powered separation of charge that underpins natural photosynthesis can be exploited for applications in photoelectrochemistry by coupling nanoscale protein photoreaction centers to man-made electrodes. Planar photoelectrochemical cells employing purple bacterial reaction centers have been constructed that produce a direct current under continuous illumination and an alternating current in response to discontinuous illumination. The present work explored the basis of the open-circuit voltage (V(OC)) produced by such cells with reaction center/antenna (RC-LH1) proteins as the photovoltaic component. It was established that an up to ~30-fold increase in V(OC) could be achieved by simple manipulation of the electrolyte connecting the protein to the counter electrode, with an approximately linear relationship being observed between the vacuum potential of the electrolyte and the resulting V(OC). We conclude that the V(OC) of such a cell is dependent on the potential difference between the electrolyte and the photo-oxidized bacteriochlorophylls in the reaction center. The steady-state short-circuit current (J(SC)) obtained under continuous illumination also varied with different electrolytes by a factor of ~6-fold. The findings demonstrate a simple way to boost the voltage output of such protein-based cells into the hundreds of millivolts range typical of dye-sensitized and polymer-blend solar cells, while maintaining or improving the J(SC). Possible strategies for further increasing the V(OC) of such protein-based photoelectrochemical cells through protein engineering are discussed.

High-resolution strain sensing on steel by Silicon-On-Insulator flexural resonators fabricated with chip-level vacuum packaging

This paper reports on the fabrication and characterization of high-resolution strain sensors for steel based on Silicon On Insulator flexural resonators manufactured with chip-level LPCVD vacuum packaging. The sensors present high sensitivity (120 Hz/μ), very high resolution (4 n), low drift, and near-perfect reversibility in bending tests performed in both tensile and compressive strain regimes. © 2013 IEEE.

Dry oxidation and vacuum annealing treatments for tuning the wetting properties of carbon nanotube arrays.

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.(1,2) These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.(2) Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.(3-5) The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

Reversible tuning of the wettability of carbon nanotube arrays: the effect of ultraviolet/ozone and vacuum pyrolysis treatments.

Among diverse types of synthetic materials, arrays of vertically aligned carbon nanotubes have attracted the most attention, mainly because of their exceptional mechanical, electrical, optical, and thermal properties. However, their wetting properties are yet to be understood. In this present study, oxygenated surface functional groups have been identified as a vital factor in controlling the wetting properties of carbon nanotube arrays. The results presented herein indeed show that a combination of ultraviolet/ozone and vacuum pyrolysis treatments can be used to vary the surface concentration of these functional groups such that the carbon nanotube array can be repeatedly switched between hydrophilic and hydrophobic.

Normal incidence p-i-n Ge heterojunction photodiodes on Si substrate grown by ultrahigh vacuum chemical vapor deposition

We report on normal incidence p-i-n heterojunction photodiodes operating in the near-infrared region and realized in pure germanium on planar silicon substrate. The diodes were fabricated by ultrahigh vacuum chemical vapor deposition at 600 degrees C without thermal annealing and allowing the integration with standard silicon processes. Due to the 0.14% residual tensile strain generated by the thermal expansion mismatch between Ge and Si, an efficiency enhancement of nearly 3-fold at 1.55 mu m and the absorption edge shifting to longer wavelength of about 40 nm are achieved in the epitaxial Ge films. The diode with a responsivity of 0.23 A/W at 1.55 mu m wavelength and a bulk dark current density of 10 mA/cm(2) is demonstrated. These diodes with high performances and full compatibility with the CMOS processes enable monolithically integrating microphotonics and microelectronics on the same chip.

The influence of low-temperature Ge seed layer on growth of high-quality Ge epilayer on Si(100) by ultrahigh vacuum chemical vapor deposition

High-quality Ge epilayer on Si(1 0 0) substrate with an inserted low-temperature Ge seed layer and a thin Si0.77Ge0.23 layer was grown by ultrahigh vacuum chemical vapor deposition. The epitaxial Ge layer with surface root-mean-square roughness of 0.7 nm and threading dislocation density of 5 x 10(5) cm(-2) was obtained. The influence of low temperature Ge seed layer on the quality of Ge epilayer was investigated. We demonstrated that the relatively higher temperature (350 degrees C) for the growth of Ge seed layer significantly improved the crystal quality and the Hall hole mobility of the Ge epilayer. (C) 2008 Elsevier B.V. All rights reserved.

Stability and photoemission characteristics for GaAs photocathodes in a demountable vacuum system

The stability and photoemission characteristics for reflection-mode GaAs photocathodes in a demountable vacuum system have been investigated by using spectral response and x-ray photoelectron spectroscopy measurements at room temperature. We find that the shape of the spectral response curve for the cathode changes with time in the vacuum system, but after applying fresh cesium to the degraded cathode, the spectral response can almost be restored. The change and restoration of curve shape are mainly attributed to the evolution of the surface barrier. We illustrate the evolution and analyze the influence of the barrier on the spectral response of the cathode. (C) 2008 American Institute of Physics.

Relaxed GexSi1-x layer formation with reduced dislocation density grown by ultrahigh vacuum chemical vapor deposition

A new alternative method to grow the relaxed Ge0.24Si0.76 layer with a reduced dislocation density by ultrahigh vacuum chemical vapor deposition is reported in this paper. A 1000-Angstrom Ge0.24Si0.76 layer was first grown on a Si(100) substrate. Then a 500-Angstrom Si layer and a subsequent 5000-Angstrom Ge0.24Si0.76 overlayer followed. All these three layers were grown at 600 degrees C. After being removed from the growth system to air, the sample was first annealed at 850 degrees C for 30 min, and then was investigated by cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy. It is shown that the 5000-Angstrom Ge0.24Si0.76 thick over layer is perfect, and most of the threading dislocations are located in the embedded thin Si layer and the lower 1000-Angstrom Ge0.24Si0.76 layer. The relaxation ratio of the over layer is deduced to be 0.8 from Raman spectroscopy.