I. Muntele

Structural Changes in Polymer Films by Fast Ion Implantation

In applications from food wrapping to solar sails, polymers films can be subjected to intense charged panicle bombardment and implantation. ETFE (ethylenetetrafluoroethylene) with high impact resistance is used for pumps, valves, tie wraps, and electrical components. PFA (tetrafluoroethylene‐per‐fluoromethoxyethylene) and FEP (tetrafluoroethylene‐hexa‐fluoropropylene) are sufficiently biocompatible to be used as transcutaneous implants since they resist damage from the ionizing space radiation, they can be used in aerospace engineering applications. PVDC (polyvinyllidene‐chloride) is used for food packaging, and combined with others plastics, improves the oxygen barrier responsible for the food preservation. Fluoropolymers are also known for their radiation dosimetry applications, dependent on the type and energy of the radiation, as well as of the beam intensity.In this work ETFE, PFA, FEP and PVDC were irradiated with ions of keV and MeV energies at several fluences and were analyzed through techniques ...

Study of lightweight Ni-Co alloy mirrors obtained by electroforming techniques

One contribution in reducing the costs of optics in space can be provided by production of ultralight mirrors. The decrease in the weight of the primary mirror of a telescope is anticipated to lead to the possibility of increasing the size of the telescopes, therefore increasing the amount and distance from which information is received. An electroplating process of ultralight replica mirrors from nickel sulfamate solution is described. Based on an experimental setup with cylindrical symmetry, flat mirrors with a diameter of 4 and 7 inches and thickness of 1 through 2 mm are made from a Ni-Co alloy. The composition of the resulting deposit is analyzed using Rutherford Backscattering Spectrometry (RBS) and Proton Induced X-ray Emission (PIXE). In order to isotopically resolve Ni and Co, 6 MeV nitrogen ions are used as projectiles in the RBS measurements. Solution parameters monitored during the deposition process using optical absorption spectrophotometry is correlated with the final concentration of Ni and Co in the deposit. Bath parameters like temperature; current density, agitation level and acidity are chosen at certain values and maintained constant from one sample to another throughout the deposition process. The purpose of the experiment is to obtain mirrors with near zero stress, and predetermined composition and hardness. This study is an intermediate step in obtaining through the same process, but with a larger scale setup, ultralight large aperture replica mirrors.

Improved Sensitivity SiC Hydrogen Sensor

We have produced silicon carbide sensors by two techniques: palladium coating and low energy palladium implantation, The palladium implantation was done at 550°C into the Si face of 6H, n-type Sic at various energies and at various fluences. The sensitivity of each sensor was measured at temperatures between 20°C to 4OOOC. The response of the Sic sensors produced by Pd implantation has revealed a completely different behavior than the Sic sensors produced by Pd deposition In the Pd deposited Sic sensors, as well as in the ones reported in the literature [ 1, 21, the current rises in the presence of hydrogen at room temperature as well as at elevated temperatures. In the case of Pd implanted Sic sensors, the current decreases in the presence of hydrogen whenever the temperature is raised above 100°C [3].

Depth Profiling of SiC Lattice Damage Using Micro-Raman Spectroscopy

Abstract : Depth profiling for the amount of lattice damage using a Confocal Micro-Raman (CMR) spectrometer is demonstrated in this paper. Samples of n-type silicon carbide were implanted with 2 MeV He and O ions at both room temperature and 500 deg C, and fluences between 10(exp 15) and 10(exp 17) ions/sq cm. Post-implantation annealing at 1000 deg C was also performed in order to study the damage evolution. Optical Absorption Spectrophotometry (OAS) was used for establishing the opacity (and therefore the probing depth) of the damaged layer to the 632.8 nm wavelength of the He-Ne laser used for CMR throughout this study. The methodology used and the results obtained are presented herein. Total dissipation of amorphous carbon islands was observed even at low annealing temperatures of the RT implanted samples, along with an increase in the size of the amorphous silicon islands.

Chemical, Mechanical and Electrical Properties of Glassy Polymeric Carbon

Glassy Polymeric Carbon (GPC) is obtained by a molding technique, in various shapes, from a phenolic resin precursor. The heat treatment of the precursor is achieved in three stages up to 1000 °C. Similar GPC materials produced in our laboratory displayed large strain to failure ratio, small thermal expansion coefficient and low density. Like all carbon forms, is attacked by oxygen, especially atomic oxygen. Nevertheless the kinetics for reaction with atmospheric oxygen is very slow. We investigated the composition and structural changes of the phenolic precursor as a function of temperature and evaluated materials stability when exposed to high temperatures in presence of hydrogen or oxygen.

Raman and FTIR studies on nanostructure formation on silicon carbide

We report experimental results following studies on the defects induced by light and heavy high-energy ion implantation into 6H p-type and n-type silicon carbide, as well as the degree of crystalline lattice recovery after annealing in high purity argon environment at 1100 and 1600°C. We implanted silicon carbide with MeV Au and Al ions at levels of 1016 and 1017 ions/cm2, and used confocal micro-Raman (MR) and Fourier-Transform Infra-Red (FTIR) optical spectroscopy techniques to characterize the silicon carbide lattice optical properties at various stages during the post-implantation annealing process. We also investigated the conditions for metallic nanoclusters formation following the destruction of the lattice during the ion implantation and influence of the thermal treatment on their evolution.