Effect of Carbon Impurity on Molybdenum Nanostructure Evolution under Helium Ion Irradiation in Extreme Conditions

The performance of plasma facing components (PFC) is of great important for the realization of prototype nuclear fusion. Tungsten has been considered as the leading high-Z PFC material for these reactors and tokamaks due to its superior thermophysical properties, high melting point, low sputtering yield, and low tritium inventory. However, its surface deteriorates significantly under helium ion irradiation in extreme (fusion) conditions and forms nanoscopic fiber like structures (fuzz) Recent studies show that the formation of fuzz nanostructure on tungsten can be suppressed by the presence of plasma impurities such as carbon and beryllium. In the present study, the effects of carbon impurity on molybdenum nanostructure evolution under extreme condition helium ion irradiation have been investigated. For mixing the carbon impurity on molybdenum surface, a mixture of helium and methane (CH4) gas has been used. Separate experiments with 100% pure helium and with mixture gas have been performed. Ion energy (100eV), ion-flux (7.2 1020 ions m-2 s-1), ion-fluence (2.6 1024 ions m-2) and target temperatures (923K) were chosen from our previous studies and fixed constant during the whole study, for all the samples. The surface modification and compositional analysis, due to 100% pure helium ion and “helium+ carbon” ion irradiations, will be studied using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), respectively. In addition, optical-reflectivity measurements will also be performed for monitoring the surface deterioration due to energetic pure helium ion and mixture “helium+carbon” ion irradiations. Our results indicate that 0.5 % carbon impurity (a mixture of 97.5 % helium and 2.5% methane gas) may prevent almost all the molybdenum fuzz formation and deposit a thin carbon layer on molybdenum surface

Effect of Helium Ions Energy on Molybdenum Surfaces Under Extreme Conditions

Plasma facing components (PFCs) in fusion devices must be able to withstand high temperatures and erosion due to incident energetic ion radiations. Tungsten has become the material of choice for PFCs due to its high strength, thermal conductivity, and low erosion rate. However, its surface deteriorates significantly under helium ion irradiation in fusion-like conditions and forms nanoscopic fiber-like structures, or fuzz. Fuzz is brittle in nature and has relatively lower thermal conductivity than that of the bulk material. Small amounts of fuzz may lead to excessive contamination of the plasma, preventing the fusion reaction from taking place. Despite recent efforts, the physical mechanism of the surface deterioration is still not clear. This necessitates finding alternative materials for PFCs. In this report, the effect of helium ion energy on molybdenum surfaces is investigated. Helium ion irradiations on mirror finished polished molybdenum samples are performed as a function of helium ion energy from 100-1600eV with fixed values of ion-flux (7.2 x 1020 ions m-2 s-1), ion-fluence (2.6 x 1024 ions m-2), and temperature (923K). The surface modifications were studied using scanning electron and atomic force microscopy along with X-ray photoelectron spectroscopy and optical-reflectivity measurements. Reduction in the “protrusion” of fuzz from the surface and fuzz density at increased energy have been seen from microscopy and optical reflectivity studies. These findings further the understanding of fuzz formation on high-Z refractory metals for fusion applications. KEYWORD

RECURRENT PREGNANCY LOSS AND ASSOCIATION OF MTHFR, PAI-1 AND ACE GENE POLYMORPHISMS IN WOMEN

Recurrent pregnancy loss (RPL) is a significant clinical problem that may occur before the 20th week of gestation. There is no general consensus on how many consecutive abortions are considered as RPL. The goal of this study is to investigate the correlation between recurrent miscarriage (RM) and common polymorphisms in angiotensin-converting enzyme (ACE), plasminogen activator inhibitor 1 (PAI-1) and Methylenetetrahydrofolate Reductase (MTHFR) genes among women experiencing RM. The literature existing in different population was searched and based on these finding we conclude that polymorphism in either one of these genes may increase chances of miscarriage. KEYWORDS: Polymorphism; Recurrent pregnancy; Plasminogen activator inhibitor 1

RECURRENT PREGNANCY LOSS AND ASSOCIATION OF MTHFR, PAI-1 AND ACE GENE POLYMORPHISMS IN WOMEN

Recurrent pregnancy loss (RPL) is a significant clinical problem that may occur before the 20th week of gestation. There is no general consensus on how many consecutive abortions are considered as RPL. The goal of this study is to investigate the correlation between recurrent miscarriage (RM) and common polymorphisms in angiotensin-converting enzyme (ACE), plasminogen activator inhibitor 1 (PAI-1) and Methylenetetrahydrofolate Reductase (MTHFR) genes among women experiencing RM. The literature existing in different population was searched and based on these finding we conclude that polymorphism in either one of these genes may increase chances of miscarriage. KEYWORDS: Polymorphism; Recurrent pregnancy; Plasminogen activator inhibitor 1

He+ ion Irradiation on Tungsten Surface in Extreme Conditions

Higher melting point (3695K), lower sputtering yield and most importantly, lower in-bulk, and co-deposit retention at elevated temperature makes tungsten (W) as a potential candidate for plasma-facing component (PFC) in the international thermonuclear experimental reactor (ITER)-divertor. Helium ion (He+) bombardment on W can cause wide variety of microstructural evolution, such as dislocation loops, helium holes/bubbles and fibre-form nanostructures (Fuzz) etc. In this work, 100 eV He+ ion irradiation, at temperature ranges from 500°C to 1000°C, will be performed on mechanically polished mirror like W surfaces. The surface modification and compositional analysis, due to ion irradiation, will be studied using Scanning electron- (SEM) and Atomic force- (AFM) microscopy and X-ray photoelectron spectroscopy (XPS), respectively. The formation of fibre-form nanostructures was observed for temperatures in the range of 650°C to 1000°C. It was also noted that the incident ion energy and the fluence, that the material underwent, were crucial parameters for fibre-form nanostructure formation

Methoxsalen loaded chitosan coated microemulsion for effective treatment of psoriasis

Methoxsalen has been used for the treatment of psoriasis. In order to develop alternative formulations for the topical administration of methoxsalen, chitosan coated microemulsion were evaluated as delivery vehicle. Microemulsions were prepared using water, soyabean oil. Egg phosphatidylcholine, ethanol and coated with chitosan. They were characterized for shape and surface morphology, droplet size and size distribution, zeta potential, pH and viscosity. The ability of the system to deliver into the skin was evaluated using dialysis membrane and human cadaver skin. The in vitro permeation data showed that the novel system cumulative amount released was 18.75 % lesser than the microemulsion. These studies clearly show that methoxsalen loaded chitosan-coated microemulsion provides control release of methoxsalen with retention on the skin. Therefore may be appropriate vehicle for topical delivery of methoxsalen.Keywords: Microemulsions; Soyabean; Methoxsalen; Chitosa

Investigating Tantalum as a Plasma-Facing Component for Nuclear Fusion Reactors

Nuclear fusion is a potential source for producing unlimited environment-friendly energy. Tungsten (W) is selected as the primary candidate material for plasma facing component in nuclear fusion reactors due to its high melting temperature (3695 K), low sputtering erosion yield and strong mechanical properties. However, recent investigations on W have confirmed that it undergoes severe surface morphology changes during low energy He plasma and/or ion irradiation similar to a harsh fusion environment. Additionally, our previous studies indicate that tantalum (Ta) may show better resistance to the harsh radiation environment and is therefore worthy of investigation. Hydrogen retention properties, specifically deuterium (D) retention in Ta, are not well documented and are extremely important safety issue for fusion reactors. Consequently, we exposed Ta to a fusion-like environment of low-energy D ions and performed thermal desorption spectroscopy (TDS). Then, the samples were rapidly loaded (to avoid possible surface oxidation) into another vacuum chamber where we performed the thermal desorption spectroscopy measurements. Our investigations indicate two binding energy values for D in Ta, i.e. 1.8 eV and 2.1 eV. We observe a higher binding energy and a higher retention rate for D in Ta than W. We also observed that our results are consistent with theoretical predictions based on the absorption of D in Ta. Our preliminary results indicate that Ta shows better resistance to nanostructure formation (fuzz) than W in a fusion environment. However, this is still an open question and part of ongoing investigations

Fluence Dependent Surface Modification on Tungsten Coatings Using Low Energy Helium Ion Irradiation at Elevated Temperatures

Nuclear fusion is the most promising renewable energy source for the near future. It can provide a large amount of energy using a very small amount of fuel, as compared with that of the coal, oil, or nuclear fission. The chain reaction in nuclear fusion produces the energy and fuel, from hydrogen isotopes available in see water. Tungsten (W) is a leading candidate material for the plasma-facing component (PFC) in nuclear fusion reactors such as ITER (international thermonuclear experimental reactor), because of its high melting point, high yield strength, low erosion and low hydrogen isotope retention. Recent studies showed deeply convoluted fiber-form nanostructures (fuzz) formation on W surface under high-flux low-energy He+ irradiation relevant to fusion conditions. The fuzz greatly degrades the mechanical, thermal, and optical properties of W. The significant enhanced surface area, and fragility of such fuzz, raise several serious concerns for its usefulness as PFC materials in fusion reactors. The fuzz can also be easily eroded and is a major concern for plasma contamination and short lifetime. In this study, we report on the effect of helium ion irradiation on the surface morphology evolution of W exposed to low energy He+ ions at constant elevated temperature. Submicron thickness W films were deposited on Silicon (100) at room temperature using RF sputtering deposition technique. Several samples were cut and were exposed to 100 eV He+ ions having a constant flux of 1.2 × 1021 ions m−2 s−1 and sample temperature (1173K). The fluence was varied in the range of 4.3 × 1024 – 1.7 × 1025 ions m−2. Post ion-irradiation samples (including pristine) were characterized using field emission scanning electron microscopy (FE-SEM), X-ray photoelectric spectroscopy (XPS), and optical reflectivity measurements for monitoring the changes in surface morphology, chemical composition, and surface roughness/optical properties, respectively. We observed a sequential enhancement in the W fuzz density, sharpness, and protrusions from the film surface, with increasing helium ion fluence. Ex-situ XPS study shows the evidence of W2O3 phase formation due to natural oxidation of W fuzz in the open atmosphere. The study is also relevant to potential applications in solar power technology and in water splitting for hydrogen production

Temperature Dependent Surface Modification of Tungsten Exposed to High-Flux Low-Energy Helium Ion Irradiation

Nuclear fusion is a great potential energy source that can provide a relatively safe and clean limitless supply of energy using hydrogen isotopes as fuel material. ITER (international thermonuclear experimental reactor) is the world first fusion reactor currently being built in France. Tungsten (W) is a prime candidate material as plasma facing component (PFC) due to its excellent mechanical properties, high melting point, and low erosion rate. However, W undergoes a severe surface morphology change when exposed to helium ion (He+) bombardment under fusion conditions. It forms nanoscopic fiber-form structures, i.e., fuzz on the surface. Fuzz is brittle and can easily contaminate the plasma, and therefore preventing the fusion chain reaction. In this study, we report on the effect of temperature on the surface morphology evolution of W coatings under low energy He+ ion irradiation, relevant to fusion conditions. Submicron thickness W films have been deposited on Si (100) at room temperature using RF sputtering deposition technique. Several samples were cut from the same wafer and exposed to 100 eV He+ ions having a constant flux of 1.2 × 1021 ions m−2 s−1 (total fluence of 4.3 × 1024 ions m−2) at several temperatures in the range of 1073 – 1273 K. During each ion irradiation experiments the applied sample temperature were constant throughout that experiment. Post ion-irradiation samples (including pristine) were characterized using field emission scanning electron microscopy (FE-SEM), X-ray photoelectric spectroscopy (XPS), and optical reflectivity measurements for monitoring the changes in surface morphology, chemical composition, and surface roughness/optical properties, respectively. Our analysis shows a sequential enhancement in W fuzz density, sharpness, and protrusions from the film surface, with increasing sample temperature, during helium ion irradiation. Ex-situ XPS study shows the evidence of W2O3 phase formation due to natural oxidation of W fuzz in the open atmosphere, for all irradiated samples. The study is significant in the understanding processes of fuzz formation on high-Z refractory metals for fusion applications. In addition, the observed W2O3 fuzz structure may have potential applications in solar power concentration technology and in water splitting for hydrogen production

IMPACT OF CHANNEL ENGINEERING (SI1-0.25GE0.25) TECHNIQUE ON GM (TRANSCONDUCTANCE) AND ITS HIGHER ORDER DERIVATIVES OF 3D CONVENTIONAL AND WAVY JUNCTIONLESS FINFETS (JLT)

The paper explores the analog analysis and higher order derivatives of drain current (ID) at gate source voltage (VGS), by introducing channel engineering technique of 3D conventional and Wavy Junctionless FinFETs (JLT) as silicon germanium  (Si1-0.25Ge0.25) device layer. In view of this, the performances are carried out for different gate length (LG) values (15-30 nm) and current characteristics determined by maintaining constant ON current (ION 10-5) (A/μm) for both devices. With respect to this, a comparison has been made between these MOS structures at molefraction x = 0.25 and it was found that the electric field is perpendicular to the current flow which induces volume inversion approach. Accordingly, for the simulation study better channel controllability over the gate is observed for Wavy structures and high ID induces as the LG scales down. With respect to this the constant ION determine ID, transconductance (gm), transconductance generation factor (TGF) and its higher order terms (g\m, and g\\m) of the devices are studied with relaxed SiGe approximation. The extensive simulation study on short channel (SC) parameters are also performed and it is observed that the Wavy JL FinFET shows less sensitivity towards short channel effects (SCEs) over conventional one, therefore the dependency of N-type doping concentration (ND = 1.7x1019 cm-3) and metal workfunction (ϕM = 4.6 eV) are responsible to achieving reduced SCEs.