High efficiency 4H-SiC betavoltaic power sources using tritium radioisotopes

NASA Astrophysics Data System (ADS)

Thomas, Christopher; Portnoff, Samuel; Spencer, M. G.

2016-01-01

Realization of an 18.6% efficient 4H-silicon carbide (4H-SiC) large area betavoltaic power source using the radioisotope tritium is reported. A 200 nm 4H-SiC P+N junction is used to collect high-energy electrons. The electron source is a titanium tritide (TiH3x) foil, or an integrated titanium tritide region formed by the diffusion of tritium into titanium. The specific activity of the source is directly measured. Dark current measured under short circuit conditions was less than 6.1 pA/cm2. Samples measured with an external tritium foil produced an open circuit voltage of 2.09 V, short circuit current of 75.47 nA/cm2, fill factor of 0.86, and power efficiency of 18.6%. Samples measured with an integrated source produced power efficiencies of 12%. Simulations were done to determine the beta spectrum (modified by self absorption) exiting the source and the electron hole pair generation function in the 4H-SiC. The electron-hole pair generation function in 4H-SiC was modeled as a Gaussian distribution, and a closed form solution of the continuity equation was used to analyze the cell performance. The effective surface recombination velocity in our samples was found to be 105-106 cm/s. Our analysis demonstrated that the surface recombination dominates the performance of a tritium betavoltaic device but that using a thin P+N junction structure can mitigate some of the negative effects.

Kinetic Investigations of SiMn Slags From Different Mn Sources

NASA Astrophysics Data System (ADS)

Kim, Pyunghwa Peace; Tangstad, Merete

2018-06-01

The kinetics of MnO and SiO2 reduction were investigated for Silicomanganese (SiMn) slags using a Thermogravimetric analysis (TGA) between 1773 K and 1923 K (1500 °C and 1650 °C) under CO atmospheric pressure. The charge materials were based on Assmang ore and HC FeMn Slag. Rate models for MnO and SiO2 reduction were applied to describe the metal-producing rates, as shown by the following equations: r_{MnO} = k_{MnO} × A × ( {a_{MnO} - {a_{Mn} }/{K_{T }}} ) r_{{{SiO}2 }} = k_{SiO2} × A × ( {a_{{{SiO}2 }} - {a_{Si} }/{K_{T }}} ). The results show that the choice of raw materials in the charge considerably affected the reduction rate of MnO and SiO2. The highest reduction rate was found to be from charges using HC FeMn slag. The difference in the driving forces was insignificant among the SiMn slags, and the similar slag viscosities could not explain the different reduction rates. Instead, the difference is attributed to small amounts of sulfur and the amount of iron in the charge. In addition, the rate models were applicable to describe the reduction of MnO and SiO2 in SiMn slags.

Influence of Si addition on the carbon partitioning process in martensitic-austenitic stainless steels

NASA Astrophysics Data System (ADS)

Huang, Q.; Volkova, O.; De Cooman, BC; Biermann, H.; Mola, J.

2018-06-01

The effect of Si on the efficiency of carbon partitioning during quenching and partitioning (Q&P) processing of stainless steels was studied. For this purpose, 2 mass-% Si was added to a Fe-13Cr-0.47C reference steel. The Si-free (reference) and Si-added steels were subjected to Q&P cycles in dilatometer. The carbon enrichment of austenite in both steels was evaluated by determining the temperature interval between the quench temperature and the martensite start temperature of secondary martensite formed during final cooling to room temperature. In Q&P cycles with comparable martensite fractions at the quench temperature, the carbon enrichment of austenite after partitioning was similar for both steels. To compare the mechanical stability of austenite, Q&P-processed specimens of both steels were tensile tested in the temperature range 20-200 °C. The quench and partitioning temperatures were room temperature and 450 °C, respectively. Si addition had no meaningful influence on mechanical stability of austenite. The results indicate that the suppression of cementite formation by Si addition to stainless steels, as confirmed by transmission electron microscopy examinations, has no noticeable influence on the carbon enrichment of austenite in the partitioning step.

High efficiency 4H-SiC betavoltaic power sources using tritium radioisotopes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, Christopher; Portnoff, Samuel; Spencer, M. G.

Realization of an 18.6% efficient 4H-silicon carbide (4H-SiC) large area betavoltaic power source using the radioisotope tritium is reported. A 200 nm 4H-SiC P{sup +}N junction is used to collect high-energy electrons. The electron source is a titanium tritide (TiH{sup 3}{sub x}) foil, or an integrated titanium tritide region formed by the diffusion of tritium into titanium. The specific activity of the source is directly measured. Dark current measured under short circuit conditions was less than 6.1 pA/cm{sup 2}. Samples measured with an external tritium foil produced an open circuit voltage of 2.09 V, short circuit current of 75.47 nA/cm{sup 2}, fill factor of 0.86,more » and power efficiency of 18.6%. Samples measured with an integrated source produced power efficiencies of 12%. Simulations were done to determine the beta spectrum (modified by self absorption) exiting the source and the electron hole pair generation function in the 4H-SiC. The electron-hole pair generation function in 4H-SiC was modeled as a Gaussian distribution, and a closed form solution of the continuity equation was used to analyze the cell performance. The effective surface recombination velocity in our samples was found to be 10{sup 5}–10{sup 6 }cm/s. Our analysis demonstrated that the surface recombination dominates the performance of a tritium betavoltaic device but that using a thin P{sup +}N junction structure can mitigate some of the negative effects.« less

Si1-yCy/Si(001) gas-source molecular beam epitaxy from Si2H6 and CH3SiH3: Surface reaction paths and growth kinetics

NASA Astrophysics Data System (ADS)

Foo, Y. L.; Bratland, K. A.; Cho, B.; Desjardins, P.; Greene, J. E.

2003-04-01

In situ surface probes and postdeposition analyses were used to follow surface reaction paths and growth kinetics of Si1-yCy alloys grown on Si(001) by gas-source molecular-beam epitaxy from Si2H6/CH3SiH3 mixtures as a function of C concentration y (0-2.6 at %) and temperature Ts (500-600 °C). High-resolution x-ray diffraction reciprocal lattice maps show that all layers are in tension and fully coherent with their substrates. Film growth rates R decrease with both y and Ts, and the rate of decrease in R as a function of y increases rapidly with Ts. In situ isotopically tagged D2 temperature-programmed desorption (TPD) measurements reveal that C segregation during steady-state Si1-yCy(001) growth results in charge transfer from Si surface dangling bonds to second-layer C atoms, which have a higher electronegativity than Si. From the TPD results, we obtain the coverage θSi*(y,Ts) of Si* surface sites with C backbonds as well as H2 desorption energies Ed from both Si and Si* surface sites. θSi* increases with increasing y and Ts in the kinetically limited segregation regime while Ed decreases from 2.52 eV for H2 desorption from Si surface sites with Si back bonds to 2.22 eV from Si* surface sites. This leads to an increase in the H2 desorption rate, and hence should yield higher film deposition rates, with increasing y and/or Ts during Si1-yCy(001) growth. The effect, however, is more than offset by the decrease in Si2H6 reactive sticking probabilities at Si* surface sites. Film growth rates R(Ts,JSi2H6,JCH3SiH3) calculated using a simple transition-state kinetic model, together with measured kinetic parameters, were found to be in excellent agreement with the experimental data.

The effect of aluminum additions on the oxidation resistance of U 3Si 2

DOE PAGES

Wood, E. Sooby; White, J. T.; Nelson, A. T.

2017-04-01

The effect of aluminum additions to U 3Si 2 is investigated in this paper as a means to improve the oxidation resistance of this nuclear fuel form. Four U-Si-Al compositions have been synthesized and characterized using scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. The onsets of breakaway oxidation are identified in air thermal ramp tests using thermogravimetric analysis. The final oxidation products following 1000° C air exposure are identified using x-ray diffraction and compared to those of UO 2 and U metal oxidized in the same manner. Finally, thermogravimetric data acquired in this study indicates that increasing amountsmore » of Al in U 3Si 2 further delays the onset of breakaway oxidation, providing enhanced oxidation resistance in air. Al 2O 3 formation on U 3Al 2Si 3 is observed following a heat treatment performed at 500° C in air, demonstrating the potential of Al additions to improve the oxidation resistance of U 3Si 2.« less

The effect of aluminum additions on the oxidation resistance of U 3Si 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wood, E. Sooby; White, J. T.; Nelson, A. T.

The effect of aluminum additions to U 3Si 2 is investigated in this paper as a means to improve the oxidation resistance of this nuclear fuel form. Four U-Si-Al compositions have been synthesized and characterized using scanning electron microscopy, energy dispersive spectroscopy, and x-ray diffraction. The onsets of breakaway oxidation are identified in air thermal ramp tests using thermogravimetric analysis. The final oxidation products following 1000° C air exposure are identified using x-ray diffraction and compared to those of UO 2 and U metal oxidized in the same manner. Finally, thermogravimetric data acquired in this study indicates that increasing amountsmore » of Al in U 3Si 2 further delays the onset of breakaway oxidation, providing enhanced oxidation resistance in air. Al 2O 3 formation on U 3Al 2Si 3 is observed following a heat treatment performed at 500° C in air, demonstrating the potential of Al additions to improve the oxidation resistance of U 3Si 2.« less

Effect of source frequency and pulsing on the SiO2 etching characteristics of dual-frequency capacitive coupled plasma

NASA Astrophysics Data System (ADS)

Kim, Hoe Jun; Jeon, Min Hwan; Mishra, Anurag Kumar; Kim, In Jun; Sin, Tae Ho; Yeom, Geun Young

2015-01-01

A SiO2 layer masked with an amorphous carbon layer (ACL) has been etched in an Ar/C4F8 gas mixture with dual frequency capacitively coupled plasmas under variable frequency (13.56-60 MHz)/pulsed rf source power and 2 MHz continuous wave (CW) rf bias power, the effects of the frequency and pulsing of the source rf power on the SiO2 etch characteristics were investigated. By pulsing the rf power, an increased SiO2 etch selectivity was observed with decreasing SiO2 etch rate. However, when the rf power frequency was increased, not only a higher SiO2 etch rate but also higher SiO2 etch selectivity was observed for both CW and pulse modes. A higher CF2/F ratio and lower electron temperature were observed for both a higher source frequency mode and a pulsed plasma mode. Therefore, when the C 1s binding states of the etched SiO2 surfaces were investigated using X-ray photoelectron spectroscopy (XPS), the increase of C-Fx bonding on the SiO2 surface was observed for a higher source frequency operation similar to a pulsed plasma condition indicating the increase of SiO2 etch selectivity over the ACL. The increase of the SiO2 etch rate with increasing etch selectivity for the higher source frequency operation appears to be related to the increase of the total plasma density with increasing CF2/F ratio in the plasma. The SiO2 etch profile was also improved not only by using the pulsed plasma but also by increasing the source frequency.

Addition of Si-Containing Gases for Anisotropic Etching of III-V Materials in Chlorine-Based Inductively Coupled Plasma

NASA Astrophysics Data System (ADS)

Gatilova, Lina; Bouchoule, Sophie; Patriarche, Gilles; Guilet, Stephane

2011-08-01

We discuss the possibility of obtaining high-aspect-ratio etching of InP materials in Cl2- and HBr-based inductively coupled plasmas (ICP) with the addition of Si-containing gases (SiH4 or SiCl4). A vertical and smooth etching profile is demonstrated in SiCl4/H2 plasma. The effect of adding of a small amount of SiH4 to a previously optimised Cl2/H2 chemistry is presented, and new SiH4/Cl2 and SiH4/HBr chemistries are proposed. Ex-situ energy-dispersive X-ray spectroscopy coupled to transmission electron microscopy (EDX-TEM) is used to analyze the composition of the thin passivation layer deposited on the etched sidewalls. We show that it consists of a Si-rich silicon oxide (Si/O˜1) in Cl2/H2/SiH4 chemistry, and is changed to nano-crystalline (nc-) Si in SiH4/Cl2 chemistry depending on the SiH4 percentage. Moreover, we show that deep anisotropic etching of InP independent of the electrode coverplate material can be obtained via a SiOx passivation mechanism with the addition of Si-containing gases.

Fabrication and characterization of Si3N4 ceramics without additives by high pressure hot pressing

NASA Technical Reports Server (NTRS)

Shimada, M.; Tanaka, A.; Yamada, T.; Koizumi, M.

1984-01-01

High pressure hot-pressing of Si3N4 without additives was performed using various kinds of Si3N4 powder as starting materials, and the relation between densification and alpha-beta phase transformation was studied. The temperature dependences of Vickers microhardness and fracture toughness were also examined. Densification of Si3N4 was divided into three stages, and it was found that densification and phase transformation of Si3N4 under pressure were closely associated. The results of the temperature dependence of Vickers microhardness indicated that the high-temperature hardness was strongly influenced not only by the density and microstructure of sintered body but also by the purity of starting powder. The fracture toughness values of Si3N4 bodies without additives were 3.29-4.39 MN/m to the 3/2 power and independent of temperature up to 1400 C.

Low temperature ECR-CVD of SiN X for III-V device passivation

NASA Astrophysics Data System (ADS)

Lee, J. W.; MacKenzie, K.; Johnson, D.; Shul, R. J.; Pearton, S. J.; Ren, F.

1998-06-01

Electron Cyclotron Resonance SiH 4/N 2 and SiH 4/NH 3 discharges have been employed for deposition of SiN X over a range of temperatures (25-120°C), source powers (200-700 W), pressures (15-40 mTorr), SiH 4 percentages (20-50%) and additional Ar flow rates (0-30 sccm). Deposition rates were in the range 100-700 Å min -1, with refractive indices of 1.7-2.3. The SiH 4/N 2 chemistry allowed a wider process window for tailoring the stress in the SiN X films, with chuck temperature, ECR source power, chamber pressure, SiH 4 composition and Ar addition all producing a transition from compressive to tensile stress, or vice-versa.

The Effect of Li Additions on Wear Properties of Al-Mg2Si Cast In-situ Composites

NASA Astrophysics Data System (ADS)

Ghorbani, M. R.; Emamy, M.; Ghiasinejad, J.; Malekan, A.

2010-06-01

Wear rate of a modified Al-Mg2Si composite was studied by the use of a conventional pin-on-disc technique. In-situ Al-Mg2Si composites (15, 20, 25 wt.%) were cast in a simple cylindrical mold. 0.3 wt.% Li was added into the molten composite to modify its microstructure. It has been found that Li addition decreases the mean size of primary Mg2Si particles. The wear behavior of different composites at different rates revealed that Li addition increases the wear properties of Al-15%Mg2Si to some extent but it did not have any significant influence on wear properties of two other composites.

C incorporation and segregation during Si 1- yC y/Si( 0 0 1 ) gas-source molecular beam epitaxy from Si 2H 6 and CH 3SiH 3

NASA Astrophysics Data System (ADS)

Foo, Y. L.; Bratland, K. A.; Cho, B.; Soares, J. A. N. T.; Desjardins, P.; Greene, J. E.

2002-08-01

We have used in situ D 2 temperature-programmed desorption (TPD) to probe C incorporation and surface segregation kinetics, as well as hydrogen desorption pathways, during Si 1- yC y(0 0 1) gas-source molecular beam epitaxy from Si 2H 6/CH 3SiH 3 mixtures at temperatures Ts between 500 and 650 °C. Parallel D 2 TPD results from C-adsorbed Si(0 0 1) wafers exposed to varying CH 3SiH 3 doses serve as reference data. Si 1- yC y(0 0 1) layer spectra consist of three peaks: first-order β 1 at 515 °C and second-order β 2 at 405 °C, due to D 2 desorption from Si monodeuteride and dideuteride phases, as well as a new second-order C-induced γ 1 peak at 480 °C. C-adsorbed Si(0 0 1) samples with very high CH 3SiH 3 exposures yielded a higher-temperature TPD feature, corresponding to D 2 desorption from surface C atoms, which was never observed in Si 1- yC y(0 0 1) layer spectra. The Si 1- yC y(0 0 1) γ 1 peak arises due to desorption from Si monodeuteride species with C backbonds. γ 1 occurs at a lower temperature than β 1 reflecting the lower D-Si * bond strength, where Si * represents surface Si atoms bonded to second-layer C atoms, as a result of charge transfer from dangling bonds. The total integrated monohydride (β 1+γ 1) intensity, and hence the dangling bond density, remains constant with y indicating that C does not deactivate surface dangling bonds as it segregates to the second-layer during Si 1- yC y(0 0 1) growth. Si * coverages increase with y at constant Ts and with Ts at constant y. The positive Ts-dependence shows that C segregation is kinetically limited at Ts⩽650 °C. D 2 desorption activation energies from β 1, γ 1 and β 2 sites are 2.52, 2.22 and 1.88 eV.

Microstructural characterisation of Al-Si cast alloys containing rare earth additions

NASA Astrophysics Data System (ADS)

Elgallad, E. M.; Ibrahim, M. F.; Doty, H. W.; Samuel, F. H.

2018-05-01

This paper presents a thorough study on the effect of rare earth elements, specifically La and Ce, on the microstructure characteristics of non-modified and Sr-modified A356 and A413 alloys. Several alloys were prepared by adding 1% La and 1% Ce either individually or in combination. Microstructural characterisation was carried out using optical microscopy, scanning electron microscopy and electron probe microanalysis as well as differential scanning calorimetry (DSC) analysis. The results showed that the individual and combined additions of La and Ce did not bring about any modification or even refinement in the eutectic Si structure. Moreover, these additions were found to negate the modification effect of Sr, particularly in the presence of La. The A356 and A413 alloys containing La and/or Ce displayed high phase volume fractions owing to the formation of Al-Si-La/Ce/(La,Ce) and Al-Ti-La/Ce intermetallic phases. DSC analysis revealed that the formation temperatures of these phases varied from 560 to 568 °C and 568 to 574 °C, respectively. This analysis also showed that the addition of La and Ce whether individually or in combination resulted in a depression in the eutectic temperature and a considerable increase in the solidification range, particularly for the A413 alloy.

Fabrication and Characteristics of an nc-Si/c-Si Heterojunction MOSFETs Pressure Sensor

PubMed Central

Zhao, Xiaofeng; Wen, Dianzhong; Li, Gang

2012-01-01

A novel nc-Si/c-Si heterojunction MOSFETs pressure sensor is proposed in this paper, with four p-MOSFETs with nc-Si/c-Si heterojunction as source and drain. The four p-MOSFETs are designed and fabricated on a square silicon membrane by CMOS process and MEMS technology where channel resistances of the four nc-Si/c-Si heterojunction MOSFETs form a Wheatstone bridge. When the additional pressure is P, the nc-Si/c-Si heterojunction MOSFETs pressure sensor can measure this additional pressure P. The experimental results show that when the supply voltage is 3 V, length-width (L:W) ratio is 2:1, and the silicon membrane thickness is 75 μm, the full scale output voltage of the pressure sensor is 15.50 mV at room temperature, and pressure sensitivity is 0.097 mV/kPa. When the supply voltage and L:W ratio are the same as the above, and the silicon membrane thickness is 45 μm, the full scale output voltage is 43.05 mV, and pressure sensitivity is 2.153 mV/kPa. Therefore, the sensor has higher sensitivity and good temperature characteristics compared to the traditional piezoresistive pressure sensor. PMID:22778646

Oxidation Resistance, Electrical and Thermal Conductivity, and Spectral Emittance of Fully Dense HfB2 and ZrB2 with SiC, TaSi2, and LaB6 Additives

DTIC Science & Technology

2012-01-26

Resistance , Electrical and Thermal Conductivity, and Spectral Emittance of Fully Dense HfB2 and ZrB2 "With SiC, TaSi2, and LaB6 Additives Sb. GRANT NUMBER... RESISTANCE , ELECTRICAL AND THERMAL CONDUCTIVITY, AND SPECTRAL EMITTANCE OF FULLY DENSE HfB2 AND ZrB2 WITH SiC, TaSi2, AND LaB6 ADDITIVES Air Force Office...thickened regions with dry 220 grit SiC sandpaper so that a low- resistance electrical connection could be achieved. A handheld multimeter was used to measure

Simultaneous Observatinos of H2O and SiO Masers Toward Known Extragalactic Water Maser Sources

NASA Astrophysics Data System (ADS)

Cho, Se-Hyung; Yoon, Dong-Hwan; Kim, Jaeheon; Byun, Do-Young; Wagner, Jan

2015-12-01

We observe ten known 22 GHz H_{2}O maser galaxies during February 19-22, 2011 using the 21 m Tamna telescope of the Korean VLBI Network and a new wide-band digital spectrometer. Simultaneously we searched for 43 GHz SiO v = 1, 2, J = 1-0 maser emission. We detect H_{2}O maser emission towards five sources (M 33, NGC 1052, NGC 1068, NGC 4258, M 82), with non-detections towards the remaining sources (UGC 3193, UGC 3789, Antennae H_{2}O-West, M 51, NGC 6323) likely due to sensitivity. Our 22 GHz spectra are consistent with earlier findings. Our simultaneous 43 GHz SiO maser search produced non-detections, yielding - for the first time - upper limits on the 43 GHz SiO maser emission in these sources at a 3 σ sensitivity level of 0.018 K-0.033 K (0.24 Jy-0.44 Jy) in a 1.75 km s^{-1} velocity resolution. Our findings suggest that any 43 GHz SiO masers in these sources (some having starburst-associated H_{2}O kilomasers) must be faint compared to the 22 GHz H_{2}O maser emission.

Ellipsometric study of Si(0.5)Ge(0.5)/Si strained-layer superlattices

NASA Technical Reports Server (NTRS)

Sieg, R. M.; Alterovitz, S. A.; Croke, E. T.; Harrell, M. J.

1993-01-01

An ellipsometric study of two Si(0.5)Ge(0.5)/Si strained-layer super lattices grown by MBE at low temperature (500 C) is presented, and results are compared with x ray diffraction (XRD) estimates. Excellent agreement is obtained between target values, XRD, and ellipsometry when one of two available Si(x)Ge(1-x) databases is used. It is shown that ellipsometry can be used to nondestructively determine the number of superlattice periods, layer thicknesses, Si(x)Ge(1-x) composition, and oxide thickness without resorting to additional sources of information. It was also noted that we do not observe any strain effect on the E(sub 1) critical point.

Single photon sources in 4H-SiC metal-oxide-semiconductor field-effect transistors

NASA Astrophysics Data System (ADS)

Abe, Y.; Umeda, T.; Okamoto, M.; Kosugi, R.; Harada, S.; Haruyama, M.; Kada, W.; Hanaizumi, O.; Onoda, S.; Ohshima, T.

2018-01-01

We present single photon sources (SPSs) embedded in 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). They are formed in the SiC/SiO2 interface regions of wet-oxidation C-face 4H-SiC MOSFETs and were not found in other C-face and Si-face MOSFETs. Their bright room-temperature photoluminescence (PL) was observed in the range from 550 to 750 nm and revealed variable multi-peak structures as well as variable peak shifts. We characterized a wide variety of their PL spectra as the inevitable variation of local atomic structures at the interface. Their polarization dependence indicates that they are formed at the SiC side of the interface. We also demonstrate that it is possible to switch on/off the SPSs by a bias voltage of the MOSFET.

Influence of CaCO3 and SiO2 additives on magnetic properties of M-type Sr ferrites

NASA Astrophysics Data System (ADS)

Huang, Ching-Chien; Jiang, Ai-Hua; Hung, Yung-Hsiung; Liou, Ching-Hsuan; Wang, Yi-Chen; Lee, Chi-Ping; Hung, Tong-Yin; Shaw, Chun-Chung; Kuo, Ming-Feng; Cheng, Chun-Hu

2018-04-01

An experiment was carried out to investigate the influence of CaCO3 and SiO2 additives on the magnetic and physical properties of M-type Sr ferrites by changing experimental parameters such as the additive composition and Ca/Si ratio. Specimens were prepared by conventional ceramic techniques. It was found that the magnetic properties (Br = 4.42 kG, iHc = 3.32 kOe and (BH)max = 4.863 MGOe) were considerably improved upon adding CaCO3 = 1.1% and SiO2 = 0.4 wt% together with Co3O4, and the mechanical properties thereof were acceptable for motor applications. It was revealed that CaCO3 and SiO2 additives led to an upswing in the magnetic properties via the enhancement of uniform grain growth, particle alignment, and the densification of Sr ferrite.

Thermally stable ohmic contacts to n-type GaAs. VII. Addition of Ge or Si to NiInW ohmic contacts

NASA Astrophysics Data System (ADS)

Murakami, Masanori; Price, W. H.; Norcott, M.; Hallali, P.-E.

1990-09-01

The effects of Si or Ge addition to NiInW ohmic contacts on their electrical behavior were studied, where the samples were prepared by evaporating Ni(Si) or Ni(Ge) pellets with In and W and annealed by a rapid thermal annealing method. An addition of Si affected the contact resistances of NiInW contacts: the resistances decreased with increasing the Si concentrations in the Ni(Si) pellets and the lowest value of ˜0.1 Ω mm was obtained in the contact prepared with the Ni-5 at. % Si pellets after annealing at temperatures around 800 °C. The contact resistances did not deteriorate during isothermal annealing at 400 °C for more than 100 h, far exceeding process requirements for self-aligned GaAs metal-semiconductor field-effect-transistor devices. In addition, the contacts were compatible with TiAlCu interconnects which have been widely used in the current Si process. Furthermore, the addition of Si to the NiInW contacts eliminated an annealing step for activation of implanted dopants and low resistance (˜0.2 Ω mm) contacts were fabricated for the first time by a ``one-step'' anneal. In contrast, an addition of Ge to the NiInW contacts did not significantly reduce the contact resistances.

Effect of Co Addition on the Microstructure, Martensitic Transformation and Shape Memory Behavior of Fe-Mn-Si Alloys

NASA Astrophysics Data System (ADS)

Maji, Bikas C.; Krishnan, Madangopal; Sujata, M.; Gouthama; Ray, Ranjit K.

2013-01-01

The effect of Co addition has been studied in Fe-30Mn-6Si- xCo ( x = 0 to 9 wt pct) shape memory alloys in terms of their microstructure, martensitic transformation and shape recovery. Microstructural investigations reveal that in Fe-Mn-Si-Co alloys, the microstructure remains single-phase austenite (γ) up to 5 pct Co and beyond that becomes two-phase comprising γ and off-stoichiometric (Fe,Co)5Mn3Si2 intermetallic π-phases. The forward γ-ɛ martensite transformation start temperature ( M S) decreases with the addition of Co up to 5 pct, and alloys containing more than 5 pct Co, show slightly higher M S possibly on account of two-phase microstructure. Unlike M S, the ɛ-γ reverse transformation start temperature ( A S) has been found to remain almost unaltered by Co addition. In general, addition of Co to Fe-Mn-Si alloys deteriorates shape recovery due to decreasing resistance to plastic yielding concomitant with the formation of stress induced ɛ martensite. However, there is an improvement in shape recovery beyond 5 pct Co addition, possibly due to the strengthening effect arising from the presence of (Fe,Co)5Mn3Si2 precipitates within the two-phase microstructure and due to higher amount of stress induced ɛ martensite.

Outflow structure and velocity field of Orion source. I. ALMA imaging of SiO isotopologue maser and thermal emission

NASA Astrophysics Data System (ADS)

Niederhofer, F.; Humphreys, E. M. L.; Goddi, C.

2012-12-01

Using Science Verification data from the Atacama Large Millimeter/Submillimeter Array (ALMA), we have identified and imaged five rotational transitions (J = 5-4 and J = 6-5) of the three silicon monoxide isotopologues 28SiO v = 0, 1, 2 and 29SiO v = 0 and 28Si18O v = 0 in the frequency range from 214 to 246 GHz towards the Orion BN/KL region. The emission of the ground-state 28SiO, 29SiO and 28Si18O shows an extended bipolar shape in the northeast-southwest direction at the position of Radio Source I, indicating that these isotopologues trace an outflow ( 18 km s-1, PA 50°, 5000 AU in diameter) that is driven by this embedded high-mass young stellar object (YSO). Whereas on small scales (10-1000 AU) the outflow from Source I has a well-ordered spatial and velocity structure, as probed by Very Long Baseline Interferometry (VLBI) imaging of SiO masers, the large scales (500-5000 AU) probed by thermal SiO with ALMA reveal a complex structure and velocity field, most likely related to the effects of the environment of the BN/KL region on the outflow emanating from Source I. The emission of the vibrationally-excited species peaks at the position of Source I. This emission is compact and not resolved at an angular resolution of 1farcs5 ( 600 AU at a distance of 420 pc). 2D Gaussian fitting to individual velocity channels locates emission peaks within radii of 100 AU, i.e. they trace the innermost part of the outflow. A narrow spectral profile and spatial distribution of the v = 1 J = 5-4 line similar to the masing v = 1 J = 1-0 transition, provide evidence for the most highly rotationally excited (frequency > 200 GHz) SiO maser emission associated with Source I known to date. The maser emission will enable studies of the Source I disk-outflow interface with future ALMA longest baselines.

Mechanical properties of {beta}-SiC pressureless sintered with Al{sub 2}O{sub 3} additions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mulla, M.A.; Krstic, V.D.

1994-01-01

Mechanical properties of pressureless sintered SiC with Al{sub 2}O{sub 3}addition were measured. The increase in fracture toughness and strength is attributed to the presence of a liquid phase which results in the formation of platelets of an {alpha}-SiC. The highest values for flexural strength and toughness were measured on samples with {approximately}10%Al{sub 2}O{sub 3} addition. Pull out, crack bridging and crack deflection are identified as the major strengthening and toughening mechanisms.

Effects of Mn addition on microstructure and hardness of Al-12.6Si alloy

NASA Astrophysics Data System (ADS)

Biswas, Prosanta; Patra, Surajit; Mondal, Manas Kumar

2018-03-01

In this work, eutectic Al-12.6Si alloy with and without manganese (Mn) have been developed through gravity casting route. The effect of Mn concentration (0.0 wt.%, 1 wt%, 2 wt% and 3 wt%) on microstructural morphology and hardness property of the alloy has been investigated. The eutectic Al-12.6 Si alloy exhibits the presence of combine plate, needle and rod-like eutectic silicon phase with very sharp corners and coarser primary silicon particles within the α-Al phase. In addition of 1wt.% of Mn in the eutectic Al-12.6Si alloy, sharp corners of the primary Si and needle-like eutectic Si are became blunt and particles size is reduced. Further, increase in Mn concentration (2.0 wt.%) in the Al-12.6Si alloy, irregular plate shape Al6(Mn,Fe) intermetallics are formed inside the α-Al phase, but the primary and eutectic phase morphology is similar to the eutectic Al-12.6Si alloy. The volume fraction of Al6(Mn,Fe) increases and Al6(Mn,Fe) particles appear as like chain structure in the alloy with 3 wt.% Mn. An increase in Mn concentration in the Al-12.6Si alloys result in the increase in bulk hardness of the alloy as an effects of microstructure modification as well as the presence of harder Al6(Mn,Fe) phase in the developed alloy.

Effects of the addition of Co, Ni or Cr on the decolorization properties of Fe-Si-B amorphous alloys

NASA Astrophysics Data System (ADS)

Zhang, Changqin; Zhu, Zhengwang; Zhang, Haifeng

2017-11-01

Fe-based amorphous alloys show great potential in degrading azo dyes and other organic pollutants, and are widely investigated as a kind of environmental-friendly materials for wastewater remediation. In this paper, the effects of Co, Ni or Cr addition on the decolorization properties of Fe-Si-B amorphous alloys were studied, and the mechanism of their different effects was analyzed. Co addition could lower the activation energy of Fe-Si-B amorphous alloys in decolorizing azo dyes, and had no weakening effect on the decolorization capability of Fe-Si-B amorphous alloys. Ni addition led to partial crystallization of Fe-Si-B amorphous alloys, and the decolorization mechanism at low temperatures changed from chemical degradation to physical adsorption. Cr addition could enhance the corrosion resistance of Fe-Si-B amorphous alloys, but the amorphous alloys completely lost the decolorization capability no matter at lower or higher temperatures. The results of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicated that the addition of Co, Ni or Cr could generate different surface structures that had significant influences on the decolorization process. Our work demonstrated that the effiecient decolorization of azo dyes by Fe-based alloys could be realized only when amorphous nature and incompact surface structure were simultaneously achieved for the alloys.

Effect of Copper and Zirconium Addition on Properties of Fe-Co-Si-B-Nb Bulk Metallic Glasses

NASA Astrophysics Data System (ADS)

Ikram, Haris; Khalid, Fazal Ahmad; Akmal, Muhammad; Abbas, Zameer

2017-07-01

In this research work, iron-based bulk metallic glasses (BMGs) have been fabricated, characterized and compared with Fe-Si alloy. BMG alloys of composition ((Fe0.6Co0.4)0.75B0.20Si0.05)96Nb4) were synthesized by suction casting technique using chilled copper die. Effect of copper and zirconium addition on magnetic, mechanical, thermal and electrochemical behavior of ((Fe0.6Co0.4)0.75B0.20Si0.05)96Nb4 BMGs was investigated. Furthermore, effect of annealing on nano-crystallization and subsequently on magnetic and mechanical behavior was also analyzed. Amorphousness of structure was evidenced by XRD analysis and microscopic visualization, whereas nano-crystallization behavior was identified by peak broadening of XRD patterns. Magnetic properties, measured by vibrating sample magnetometer, were found to be improved for as-cast BMG alloys by copper addition and further enhanced by nano-crystallization after annealing. Mechanical properties were observed to be increased by zirconium addition while slightly declined by copper addition. Potentiodynamic polarization analysis manifested the positive role of zirconium in enhancing corrosion resistance of BMGs in acidic, basic and brine mediums. Moreover, mechanical properties and corrosion analysis results affirmed the superiority of BMG alloys over Fe-Si alloy.

Ca Addition Effects on the Microstructure, Tensile and Corrosion Properties of Mg Matrix Alloy Containing 8 wt.% Mg2Si

NASA Astrophysics Data System (ADS)

Lotfpour, M.; Emamy, M.; Dehghanian, C.; Pourbahari, B.

2018-02-01

The microstructure, tensile properties and corrosion behavior of the Mg-8 wt.% Mg2Si-x%Ca alloy have been studied by the use of optical microscopy, scanning electron microscopy equipped with energy-dispersive spectroscopy, x-ray diffraction, standard tensile testing, polarization test and electrochemical impedance spectroscopy (EIS) measurements. Microstructural studies indicated that Ca modifies both primary and eutectic Mg2Si phase. It was found that the average size of primary Mg2Si particles is about 60 μm, which is dropped by about 82% in the alloy containing 0.05 wt.% Ca. By the addition of different Ca contents, Ca-rich intermetallics (i.e., CaSi2 and CaMgSi) were formed. The modification mechanism of adding Ca during solidification was found to be due to the strong effect of CaMgSi phase as a heterogonous nucleation site, apart from CaSi2 which was reported before, for Mg2Si intermetallics. Tensile testing results ascertained that Ca addition enhances both ultimate tensile strength (UTS) and elongation values. The optimum amount of Ca was found to be 0.1 wt.%, which improved UTS and elongation values from about 130 MPa and 2% to 165 MPa and 5.5%, whereas more Ca addition (i.e., 3 wt.%) reduced the tensile properties of the alloy to about 105 MPa and 1.8%, which can be due to the formation of CaMgSi intermetallics with deteriorating needle-like morphology. Polarization and EIS tests also showed that the Mg-3%Si-0.5%Ca alloy pronounces as the best anti-corrosion alloy. Nevertheless, further added Ca (up to 3 wt.%) deteriorated the corrosion resistance due to predominance of worse galvanic coupling effect stemmed from the presence of stronger CaMgSi cathode in comparison with Mg2Si. With higher Ca additions, an adverse effect was seen on corrosion resistance of the Mg-3%Si alloy, as a result of forming a weak film on the alloy specimen surface.

The effect of nano-SiC on characteristics of ADC12/nano-SiC composite with Sr and TiB addition produced by stir casting process

NASA Astrophysics Data System (ADS)

Anne Zulfia, S.; Salshabia, Nadella; Dhaneswara, Donanta; Utomo, Budi Wahyu

2018-05-01

ADC12 reinforced nano SiC has been successfully produced by stir casting process. Nano SiC was added into ADC12 alloy varied from 0.05 to 0.3 vf-% while Al-5Ti-1B and Sr were kept constant at 0.04 and 0.02 wt-% respectively to all composites. Mg was added 10 wt% to improve reinforce's wettability. The addition of Al-5Ti-1B to the alloy was as grain refiner while Sr was added to modify Mg2Si. All composites were characterized both microstructures analysis and mechanical properties include tensile strength, hardness, wear rate, impact strength, and porosity. The highest properties of composites was obtained at 0.3 vf-% nano SiC addition with UTS of 155.4 MPa, hardness of 46.16 HRB, impact strength of 0.22 J/mm2, and wear rate of 1.71 × 10-5 mm3/m. Tensile strength and hardness increased as grain size and porosities decreased. The highest wear resistance was investigated on the composition with the highest hardness. Impact strength decreased due to increasing volume fraction of nano-SiC. The phases present in microsturucture was dominantly Mg2Si which also affected mechanical properties of these composites.

10 CFR 1.3 - Sources of additional information.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 10 Energy 1 2010-01-01 2010-01-01 false Sources of additional information. 1.3 Section 1.3 Energy NUCLEAR REGULATORY COMMISSION STATEMENT OF ORGANIZATION AND GENERAL INFORMATION Introduction § 1.3 Sources of additional information. (a) A statement of the NRC's organization, policies, procedures...

Flexible Solar Cells Using Doped Crystalline Si Film Prepared by Self-Biased Sputtering Solid Doping Source in SiCl4/H2 Microwave Plasma.

PubMed

Hsieh, Ping-Yen; Lee, Chi-Young; Tai, Nyan-Hwa

2016-02-01

We developed an innovative approach of self-biased sputtering solid doping source process to synthesize doped crystalline Si film on flexible polyimide (PI) substrate via microwave-plasma-enhanced chemical vapor deposition (MWPECVD) using SiCl4/H2 mixture. In this process, P dopants or B dopants were introduced by sputtering the solid doping target through charged-ion bombardment in situ during high-density microwave plasma deposition. A strong correlation between the number of solid doping targets and the characteristics of doped Si films was investigated in detail. The results show that both P- and B-doped crystalline Si films possessed a dense columnar structure, and the crystallinity of these structures decreased with increasing the number of solid doping targets. The films also exhibited a high growth rate (>4.0 nm/s). Under optimal conditions, the maximum conductivity and corresponding carrier concentration were, respectively, 9.48 S/cm and 1.2 × 10(20) cm(-3) for P-doped Si film and 7.83 S/cm and 1.5 × 10(20) cm(-3) for B-doped Si film. Such high values indicate that the incorporation of dopant with high doping efficiency (around 40%) into the Si films was achieved regardless of solid doping sources used. Furthermore, a flexible crystalline Si film solar cell with substrate configuration was fabricated by using the structure of PI/Mo film/n-type Si film/i-type Si film/p-type Si film/ITO film/Al grid film. The best solar cell performance was obtained with an open-circuit voltage of 0.54 V, short-circuit current density of 19.18 mA/cm(2), fill factor of 0.65, and high energy conversion of 6.75%. According to the results of bending tests, the critical radius of curvature (RC) was 12.4 mm, and the loss of efficiency was less than 1% after the cyclic bending test for 100 cycles at RC, indicating superior flexibility and bending durability. These results represent important steps toward a low-cost approach to high-performance flexible crystalline Si film

Synthesis of high-performance Li2FeSiO4/C composite powder by spray-freezing/freeze-drying a solution with two carbon sources

NASA Astrophysics Data System (ADS)

Fujita, Yukiko; Iwase, Hiroaki; Shida, Kenji; Liao, Jinsun; Fukui, Takehisa; Matsuda, Motohide

2017-09-01

Li2FeSiO4 is a promising cathode active material for lithium-ion batteries due to its high theoretical capacity. Spray-freezing/freeze-drying, a practical process reported for the synthesis of various ceramic powders, is applied to the synthesis of Li2FeSiO4/C composite powders and high-performance Li2FeSiO4/C composite powders are successfully synthesized by using starting solutions containing both Indian ink and glucose as carbon sources followed by heating. The synthesized composite powders have a unique structure, composed of Li2FeSiO4 nanoparticles coated with a thin carbon layer formed by the carbonization of glucose and carbon nanoparticles from Indian ink. The carbon layer enhances the electrochemical reactivity of the Li2FeSiO4, and the carbon nanoparticles play a role in the formation of electron-conducting paths in the cathode. The composite powders deliver an initial discharge capacity of 195 and 137 mAh g-1 at 0.1 C and 1 C, respectively, without further addition of conductive additive. The discharge capacity at 1 C is 72 mAh g-1 after the 100th cycle, corresponding to approximately 75% of the capacity at the 2nd cycle.

Comparison Study on Additive Manufacturing (AM) and Powder Metallurgy (PM) AlSi10Mg Alloys

NASA Astrophysics Data System (ADS)

Chen, B.; Moon, S. K.; Yao, X.; Bi, G.; Shen, J.; Umeda, J.; Kondoh, K.

2018-02-01

The microstructural and mechanical properties of AlSi10Mg alloys fabricated by additive manufacturing (AM) and powder metallurgy (PM) routes were investigated and compared. The microstructures were examined by scanning electron microscopy assisted with electron-dispersive spectroscopy. The crystalline features were studied by x-ray diffraction and electron backscatter diffraction. Room-temperature tensile tests and Vickers hardness measurements were performed to characterize the mechanical properties. It was found that the AM alloy had coarser Al grains but much finer Si precipitates compared with the PM alloy. Consequently, the AM alloy showed more than 100% increment in strength and hardness compared with the PM alloy due to the presence of ultrafine forms of Si, while exhibiting moderate ductility.

Effects of Ti and La Additions on the Microstructures and Mechanical Properties of B-Refined and Sr-Modified Al-11Si Alloys

NASA Astrophysics Data System (ADS)

Li, Chenlin; Pan, Ye; Lu, Tao; Jing, Lijun; Pi, Jinhong

2018-03-01

The effects of Ti and La additions on the microstructures and mechanical properties of B-refined and Sr-modified Al-11Si alloys were investigated in the present work. The interactions among Ti, La, B and Sr elements were discussed employing microstructure observation, thermal analysis and tensile test, respectively. It was found that the addition of 0.05 wt% B induces a transformation of eutectic Si from finely fibrous to coarsely plate-like morphology in the Al-11Si alloy with 0.02 wt%Sr modification, owing to the poisoning of IIT mechanism, and the eutectic Si grows only with TPRE mechanism. Both titanium and lanthanum can neutralize the co-poisoning effect between Sr and B in the Al-11Si alloy, but the neutralizing effect of La is dependent on the addition sequence. The combinative addition of La and B elements promotes the effective refinement of α-Al grains, but an inhomogeneous modification of eutectic Si phases is also observed, leading to a slightly decrease in the elongation.

Influence of Li₂Sb Additions on Microstructure and Mechanical Properties of Al-20Mg₂Si Alloy.

PubMed

Yu, Hong-Chen; Wang, Hui-Yuan; Chen, Lei; Zha, Min; Wang, Cheng; Li, Chao; Jiang, Qi-Chuan

2016-03-29

It is found that Li₂Sb compound can act as the nucleus of primary Mg₂Si during solidification, by which the particle size of primary Mg₂Si decreased from ~300 to ~15-25 μm. Owing to the synergistic effect of the Li₂Sb nucleus and adsorption-poisoning of Li atoms, the effect of complex modification of Li-Sb on primary Mg₂Si was better than that of single modification of Li or Sb. When Li-Sb content increased from 0 to 0.2 and further to 0.5 wt.%, coarse dendrite changed to defective truncated octahedron and finally to perfect truncated octahedral shape. With the addition of Li and Sb, ultimate compression strength (UCS) of Al-20Mg₂Si alloys increased from ~283 to ~341 MPa and the yield strength (YS) at 0.2% offset increased from ~112 to ~179 MPa while almost no change was seen in the uniform elongation. Our study offers a simple method to control the morphology and size of primary Mg₂Si, which will inspire developing new Al-Mg-Si alloys with improved mechanical properties.

Tandem Solar Cells Using GaAs Nanowires on Si: Design, Fabrication, and Observation of Voltage Addition.

PubMed

Yao, Maoqing; Cong, Sen; Arab, Shermin; Huang, Ningfeng; Povinelli, Michelle L; Cronin, Stephen B; Dapkus, P Daniel; Zhou, Chongwu

2015-11-11

Multijunction solar cells provide us a viable approach to achieve efficiencies higher than the Shockley-Queisser limit. Due to their unique optical, electrical, and crystallographic features, semiconductor nanowires are good candidates to achieve monolithic integration of solar cell materials that are not lattice-matched. Here, we report the first realization of nanowire-on-Si tandem cells with the observation of voltage addition of the GaAs nanowire top cell and the Si bottom cell with an open circuit voltage of 0.956 V and an efficiency of 11.4%. Our simulation showed that the current-matching condition plays an important role in the overall efficiency. Furthermore, we characterized GaAs nanowire arrays grown on lattice-mismatched Si substrates and estimated the carrier density using photoluminescence. A low-resistance connecting junction was obtained using n(+)-GaAs/p(+)-Si heterojunction. Finally, we demonstrated tandem solar cells based on top GaAs nanowire array solar cells grown on bottom planar Si solar cells. The reported nanowire-on-Si tandem cell opens up great opportunities for high-efficiency, low-cost multijunction solar cells.

Using Si depletion in aerosol to identify the sources of crustal dust in two Chinese megacities

NASA Astrophysics Data System (ADS)

Zhao, Qing; He, Kebin; Rahn, Kenneth A.; Ma, Yongliang; Yang, Fumo; Duan, Fengkui

2010-07-01

Depletion of Si in transported dust has been recognized for many years. It can be used to distinguish between transported and local dust in cities, although it rarely has been. Here we use the variations of the Si/Al ratio in 15 months of continuous PM 2.5 samples at Beijing (northern China) and Chongqing (southwestern China) to reveal the seasonal patterns of their dust sources. For both cities, peaks of concentration for Si and Al in PM 2.5 corresponded with minima of Si/Al, and could often be linked to pulsed air flow from deserts to the northwest. With significant depletion (up to 80%) and homogeneous distribution at urban and rural sites, Si/Al showed a clear seasonal evolution, which decreased from spring to summer, increased from fall to winter, and collapsed during Chinese Spring Festival, indicating the dominance of transported dust, local fugitive dust and firework influence, respectively. The low ratios implied that desert dust is a common source during spring at Chongqing, whereas its presence during cold season at Beijing was also more frequent than expected. Failing to recognize the depletion of Si may lead to an overestimate of desert dust by 15%-65% when using the average abundance of Al in crust (6%-8%), as in previous studies. The difference in Si/Al ratio between local and transported dust implies that >60% of the dust at Beijing came from outside the city during the springs of 2004-2006. This result can help resolve the contradictory findings on this topic that have been presented earlier.

Strength and microstructure of sintered Si3N4 with rare-earth-oxide additions

NASA Technical Reports Server (NTRS)

Sanders, W. A.; Mieskowski, D. M.

1985-01-01

Room temperature, 700-, 1000-, 1200-, and 1370-C examinations of the effect of 1.7-2.6 mol pct rare earth oxide additions to sintered Si3N4 are conducted. While the room temperature-1000 C bend strengths were higher for this material with Y2O3 additions than with CeO2, La2O3, or Sm2O3, the reverse was true at 1200-1370 C. This phenomenon is explained on the basis of microstructural differences, since quantitative microscopy of SEM replicas showed the Si3N4-Y2O3 composition to contain both a higher percentage of elongated grains and a coarser microstructure than the other three alternatives. The elongated grains appear to increase this composition's low temperature strength irrespective of microstructural coarseness; this coarseness, however, decreases strength relative to the other compositions at higher temperatures.

Effects of Additives on Electrochemical Growth of Cu Film on Co/SiO2/Si Substrate by Alternating Underpotential Deposition of Pb and Surface-Limited Redox Replacement by Cu

NASA Astrophysics Data System (ADS)

Fang, J. S.; Lin, L. Y.; Wu, C. L.; Cheng, Y. L.; Chen, G. S.

2017-11-01

The effects of additives to an acidic electrolyte for electrochemical deposition of copper film to prevent corrosion of the Co/SiO2/Si substrate have been investigated. A sacrificial Pb layer was formed by underpotential deposition (UPD), then a Cu layer was prepared using surface-limited redox replacement (SLRR) to exchange the UPD-Pb layer in an acidic copper electrolyte with trisodium citrate, sodium perchlorate, and ethylenediamine as additives. The additives significantly affected the replacement of UPD-Pb by Cu and prevented galvanic corrosion of the Co/SiO2/Si substrate in the acidic Cu electrolyte. The results showed that both sodium perchlorate and ethylenediamine reduced the corrosion of the Co substrate and resulted in Cu film with low electrical resistivity. However, residual Pb was present in the Cu film when using trisodium citrate, as the citrate ions slowed copper displacement. The proposed sequential UPD-Pb and SLRR-Cu growth method may enable electrochemical deposition for fabrication of Cu interconnects on Co substrate from acidic Cu electrolyte.

A FEATURE MOVIE OF SiO EMISSION 20-100 AU FROM THE MASSIVE YOUNG STELLAR OBJECT ORION SOURCE I

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matthews, L. D.; Greenhill, L. J.; Goddi, C.

2010-01-01

We present multi-epoch Very Long Baseline Array imaging of the {sup 28}SiO v = 1 and v = 2, J = 1-0 maser emission toward the massive young stellar object (YSO) Orion Source I. Both SiO transitions were observed simultaneously with an angular resolution of approx0.5 mas (approx0.2 AU for d = 414 pc) and a spectral resolution of approx0.2 km s{sup -1}. Here we explore the global properties and kinematics of the emission through two 19-epoch animated movies spanning 21 months (from 2001 March 19 to 2002 December 10). These movies provide the most detailed view to date ofmore » the dynamics and temporal evolution of molecular material within approx20-100 AU of a massive (approx>8 M{sub sun}) YSO. As in previous studies, we find that the bulk of the SiO masers surrounding Source I lie in an X-shaped locus; the emission in the south and east arms is predominantly blueshifted, and emission in the north and west is predominantly redshifted. In addition, bridges of intermediate-velocity emission are observed connecting the red and blue sides of the emission distribution. We have measured proper motions of over 1000 individual maser features and found that these motions are characterized by a combination of radially outward migrations along the four main maser-emitting arms and motions tangent to the intermediate-velocity bridges. We interpret the SiO masers as arising from a wide-angle bipolar wind emanating from a rotating, edge-on disk. The detection of maser features along extended, curved filaments suggests that magnetic fields may play a role in launching and/or shaping the wind. Our observations appear to support a picture in which stars with masses as high as at least 8 M{sub sun} form via disk-mediated accretion. However, we cannot yet rule out that the Source I disk may have been formed or altered following a recent close encounter.« less

Effects of Combining Na and Sr additions on Eutectic Modification in Al-Si alloy

NASA Astrophysics Data System (ADS)

Zhu, G. L.; Gu, N. J.; Zhou, B. J.

2017-09-01

Experiments were designed to investigate the effects of strontium and sodium modified on the eutectic silicon for Al-Si alloy. It was found that combining addition of Na and Sr did not appear to cause deleterious interactions of modification, at at the same time, Sr-Na was fairly constant with holding time and without obvious modification fading. Addition of Na-Sr modifier could take effect quickly and decrease incubation period.

Liquid-phase growth of few-layered graphene on sapphire substrates using SiC micropowder source

NASA Astrophysics Data System (ADS)

Maruyama, Takahiro; Yamashita, Yutaka; Saida, Takahiro; Tanaka, Shin-ichiro; Naritsuka, Shigeya

2017-06-01

We demonstrated direct synthesis of graphene films consisting of a few layers (few-layered graphene) on sapphire substrates by liquid-phase growth (LPG), using liquid Ga as the melt and SiC micropowder as the source material. When the dissolution temperature was above 700 °C, almost all Si atoms of SiC diffused into the Ga melt and only carbon atoms remained at the interface beneath the liquid Ga. Above 800 °C, X-ray photoelectron spectra showed that most of the remaining carbon was graphitized. When the dissolution temperature was 1000 °C, Raman spectra showed that few-layered graphene films grew on the sapphire substrates.

Synergistic Effect of MoS2 and SiO2 Nanoparticles as Lubricant Additives for Magnesium Alloy–Steel Contacts

PubMed Central

Xie, Hongmei; Jiang, Bin; Hu, Xingyu; Peng, Cheng; Guo, Hongli; Pan, Fusheng

2017-01-01

The tribological performances of the SiO2/MoS2 hybrids as lubricant additives were explored by a reciprocating ball-on-flat tribometer for AZ31 magnesium alloy/AISI 52100 bearing steel pairs. The results demonstrated that the introduction of SiO2/MoS2 hybrids into the base oil exhibited a significant reduction in the friction coefficient and wear volume as well as an increase in load bearing capacity, which was better than the testing results of the SiO2 or MoS2 nanolubricants. Specifically, the addition of 0.1 wt % nano-SiO2 mixed with 1.0 wt % nano-MoS2 into the base oil reduced the friction coefficient by 21.8% and the wear volume by 8.6% compared to the 1.0 wt % MoS2 nanolubricants. The excellent lubrication behaviors of the SiO2/MoS2 hybrid nanolubricants can be explained by the micro-cooperation of different nanoparticles with disparate morphology and lubrication mechanisms. PMID:28644394

Effect of Sn addition on glassy Si-Te bulk sample

NASA Astrophysics Data System (ADS)

Babanna, Jagannatha K.; Roy, Diptoshi; Varma, Sreevidya G.; Asokan, Sundarrajan; Das, Chandasree

2018-05-01

Bulk Si20Te79Sn1 glass is prepared by melt-quenching method, amorphous nature of the as-quenched glass is confirmed by XRD. I-V characteristics reveals that Si20Te79Sn1 bulk sample exhibits threshold type electrical switching behavior. The thermal parameters such as crystallization temperature, glass transition temperature are obtained using differential scanning calorimetry. The crystalline peak study of the sample annealed at crystallization temperature for 2 hr shows that the Sn atom interact with Si or Te but do not interact with the Si-Te matrix in a greater extent and it forms a separate phase network individually.

Effect of Y addition on crystallization behavior and soft-magnetic properties of Fe78Si9B13 ribbons

NASA Astrophysics Data System (ADS)

Zhanwei, Liu; Dunbo, Yu; Kuoshe, Li; Yang, Luo; Chao, Yuan; Zilong, Wang; Liang, Sun; Kuo, Men

2017-08-01

A series of amorphous Fe-Si-B ribbons with various Y addition were prepared by melt-spinning. The effect of Y addition on crystallization behavior, thermal and magnetic properties was systematically investigated. With the increase of Y content, the initial crystallization temperature shifted to a higher temperature, indicating that the thermal stability of amorphous state in Fe-Si-B-Y ribbon is enhanced compared to that of Fe-Si-B alloy. Meanwhile, compared to the two exothermic peaks in the samples with lower Y content, a new exothermic peak was found in the ribbons with Y content higher than 1 at%, which corresponded to the decomposition of metastable Fe3B phase. Among all the alloys, Fe76.5Si9B13Y1.5 alloy exhibits optimized magnetic properties, with high saturation magnetization Ms of 187 emu/g and low coercivity HcJ of 7.6 A/m.

Heavily boron-doped Si layers grown below 700 C by molecular beam epitaxy using a HBO2 source

NASA Technical Reports Server (NTRS)

Lin, T. L.; Fathauer, R. W.; Grunthaner, P. J.

1989-01-01

Boron doping in Si layers grown by molecular beam epitaxy (MBE) at 500-700 C using an HBO2 source has been studied. The maximum boron concentration without detectable oxygen incorporation for a given substrate temperature and Si growth rate has been determined using secondary-ion mass spectrometry analysis. Boron present in the Si MBE layers grown at 550-700 C was found to be electrically active, independent of the amount of oxygen incorporation. By reducing the Si growth rate, highly boron-doped layers have been grown at 600 C without detectable oxygen incorporation.

The source of dissolved silicon in soil surface solutions of a temperate forest ecosystem: Ge/Si and Si isotope ratios as biogeochemical tracers

NASA Astrophysics Data System (ADS)

Cornelis, J.; Delvaux, B.; Cardinal, D.; André, L.; Ranger, J.; Opfergelt, S.

2010-12-01

solutions evolve towards lighter values (-1.38 and -2.05 ‰) and higher Ge/Si ratios (2.7 µmol/mol) relative to granite bedrock. This suggests a partial dissolution of 28Si and Ge-enriched secondary clays minerals incorporated by bioturbation in organic-rich horizons, with a fractionation releasing preferentially light Si isotopes. Without considering that organic acids promote dissolution of minerals, clay minerals detected in the organic layer (vermiculite, chlorite, illite and Ca-montmorillonite) are not stable and could have been partially dissolved and transformed in the chemical environment of forest floor. Sources of H4SiO4 in forest floor solutions are influenced by tree species which control the extent of clay-sized minerals mixed in organic horizons by bioturbation and, to a lesser extent, the Si recycling by forest vegetation.

Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process

NASA Astrophysics Data System (ADS)

Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

2017-11-01

The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

Effect of pH and added slag on the extractability of Si in two Si-deficient sugarcane soils.

PubMed

Haynes, Richard J; Zhou, Ya-Feng

2018-02-01

The effects of increasing pH on the adsorption and extractability of Si in two Si-deficient Australian sugarcane soils was investigated and the effects of increasing rates of fertilizer Si (as blast furnace slag) on pH and extractable Si were also examined. Equilibrium studies showed that maximum adsorption of Si by the two soils occurred in the pH range 9-10. When soil pH was increased from 5.0 to 6.5, subsequent adsorption of Si by the two soils, as measured by adsorption isotherms, increased. After incubation with progressive lime additions there was a decline in CaCl 2 - extractable Si due to its increased adsorption and an increase in acid (H 2 SO 4 - and acetic acid)-extractable (mainly adsorbed) Si. The increase in acid extractable Si was greater than the decrease in CaCl 2 - extractable Si suggesting a supply from an additional source. Alkali (Na 2 CO 3 and Tiron)-extractable Si decreased greatly with increasing pH suggesting dissolution of the amorphous (mainly biogenic) pool of silica was occurring with increasing pH. When increasing rates of slag were incubated with the soils, pH, CaCl 2 - and acid- extractable Si were all increased because upon dissolution slags release both silicic acid and OH - ions. There was, therefore, a positive relationship between extractable Si and soil pH. However, Na 2 CO 3 - and Tiron-extractable Si decreased with increasing slag rates (and increasing soil pH) suggesting dissolution of the biogenic pool of soil Si. It was concluded that future research needs to examine the desorption potential of adsorbed Si and the effects of liming on dissolution of the biogenic pool of soil silica under field conditions. Copyright © 2017 Elsevier Ltd. All rights reserved.

Influence of Si and N additions on structure and phase stability of Ge(2)Sb(2)Te(5) thin films.

PubMed

Kölpin, Helmut; Music, Denis; Laptyeva, Galyna; Ghadimi, Reza; Merget, Florian; Richter, Silvia; Mykhaylonka, Ruslàn; Mayer, Joachim; Schneider, Jochen M

2009-10-28

The influence of Si and N in Ge(2)Sb(2)Te(5) (space group [Formula: see text]) on structure and phase stability thereof was studied experimentally by thin film growth and characterization as well as theoretically by ab initio calculations. It was found that Si and N most probably accumulate in the amorphous matrix embedding Ge(2)Sb(2)Te(5) grains. The incorporation of Si and N in these samples causes an increase of the crystallization temperature and the formation of finer grains. N is more efficient in increasing the crystallization temperature and in reducing the grain size than Si which can be understood based on the bonding analysis. The incorporation of both Si and N in Ge(2)Sb(2)Te(5) is energetically unfavourable, leading to finer grains and larger crystallization temperatures. While in the case of Si additions no significant changes in bonding are observed, N additions appear to enable the formation of strong Te-N bonds in the amorphous matrix, which are shown to be almost twice as strong as the strongest bonds in unalloyed Ge(2)Sb(2)Te(5).

Reduction in secondary dendrite arm spacing in cast eutectic Al-Si piston alloys by cerium addition

NASA Astrophysics Data System (ADS)

Ahmad, R.; Asmael, M. B. A.; Shahizan, N. R.; Gandouz, S.

2017-01-01

The effects of Ce on the secondary dendrite arm spacing (SDAS) and mechanical behavior of Al-Si-Cu-Mg alloys were investigated. The reduction of SDAS at different Ce concentrations was evaluated in a directional solidification experiment via computer-aided cooling curve thermal analysis (CA‒CCTA). The results showed that 0.1wt%-1.0wt% Ce addition resulted in a rapid solidification time, Δ t s, and low solidification temperature, Δ T S, whereas 0.1wt% Ce resulted in a fast solidification time, Δ t a-Al, of the α-Al phase. Furthermore, Ce addition refined the SDAS, which was reduced to approximately 36%. The mechanical properties of the alloys with and without Ce were investigated using tensile and hardness tests. The quality index ( Q) and ultimate tensile strength of (UTS) Al-Si-Cu-Mg alloys significantly improved with the addition of 0.1wt% Ce. Moreover, the base alloy hardness was improved with increasing Ce concentration.

Sintering Behavior of Spark Plasma Sintered SiC with Si-SiC Composite Nanoparticles Prepared by Thermal DC Plasma Process.

PubMed

Yu, Yeon-Tae; Naik, Gautam Kumar; Lim, Young-Bin; Yoon, Jeong-Mo

2017-11-25

The Si-coated SiC (Si-SiC) composite nanoparticle was prepared by non-transferred arc thermal plasma processing of solid-state synthesized SiC powder and was used as a sintering additive for SiC ceramic formation. Sintered SiC pellet was prepared by spark plasma sintering (SPS) process, and the effect of nano-sized Si-SiC composite particles on the sintering behavior of micron-sized SiC powder was investigated. The mixing ratio of Si-SiC composite nanoparticle to micron-sized SiC was optimized to 10 wt%. Vicker's hardness and relative density was increased with increasing sintering temperature and holding time. The relative density and Vicker's hardness was further increased by reaction bonding using additional activated carbon to the mixture of micron-sized SiC and nano-sized Si-SiC. The maximum relative density (97.1%) and Vicker's hardness (31.4 GPa) were recorded at 1800 °C sintering temperature for 1 min holding time, when 0.2 wt% additional activated carbon was added to the mixture of SiC/Si-SiC.

Effects of Interface Coating and Nitride Enhancing Additive on Properties of Hi-Nicalon SiC Fiber Reinforced Reaction-Bonded Silicon Nitride Composites

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishana T.; Hull, David R.; Eldridge, Jeffrey I.; Babuder, Raymond

2000-01-01

Strong and tough Hi-Nicalon SiC fiber reinforced reaction-bonded silicon nitride matrix composites (SiC/ RBSN) have been fabricated by the fiber lay-up approach. Commercially available uncoated and PBN, PBN/Si-rich PBN, and BN/SiC coated SiC Hi-Nicalon fiber tows were used as reinforcement. The composites contained approximately 24 vol % of aligned 14 micron diameter SiC fibers in a porous RBSN matrix. Both one- and two-dimensional composites were characterized. The effects of interface coating composition, and the nitridation enhancing additive, NiO, on the room temperature physical, tensile, and interfacial shear strength properties of SiC/RBSN matrix composites were evaluated. Results indicate that for all three coated fibers, the thickness of the coatings decreased from the outer periphery to the interior of the tows, and that from 10 to 30 percent of the fibers were not covered with the interface coating. In the uncoated regions, chemical reaction between the NiO additive and the SiC fiber occurs causing degradation of tensile properties of the composites. Among the three interface coating combinations investigated, the BN/SiC coated Hi-Nicalon SiC fiber reinforced RBSN matrix composite showed the least amount of uncoated regions and reasonably uniform interface coating thickness. The matrix cracking stress in SiC/RBSN composites was predicted using a fracture mechanics based crack bridging model.

Influence of SiO2 Addition on Properties of PTFE/TiO2 Microwave Composites

NASA Astrophysics Data System (ADS)

Yuan, Ying; Wang, Jie; Yao, Minghao; Tang, Bin; Li, Enzhu; Zhang, Shuren

2018-01-01

Composite substrates for microwave circuit applications have been fabricated by filling polytetrafluoroethylene (PTFE) polymer matrix with ceramic powder consisting of rutile TiO2 ( D 50 ≈ 5 μm) partially substituted with fused amorphous SiO2 ( D 50 ≈ 8 μm) with composition x vol.% SiO2 + (50 - x) vol.% TiO2 ( x = 0, 3, 6, 9, 12), and the effects of SiO2 addition on characteristics such as the density, moisture absorption, microwave dielectric properties, and thermal properties systematically investigated. The results show that the filler was well distributed throughout the matrix. High dielectric constant ( ɛ r > 7.19) and extremely low moisture absorption (<0.02%) were obtained, resulting from the relatively high density of the composites. The ceramic particles served as barriers and improved the thermal stability of the PTFE polymer, retarding its decomposition. The temperature coefficient of dielectric constant ( τ ɛ ) of the composites shifted toward the positive direction (from - 309 ppm/°C to - 179 ppm/°C) as the SiO2 content was increased, while the coefficient of thermal expansion remained almost unchanged (˜ 35 ppm/°C).

SiC JFET Transistor Circuit Model for Extreme Temperature Range

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.

2008-01-01

A technique for simulating extreme-temperature operation of integrated circuits that incorporate silicon carbide (SiC) junction field-effect transistors (JFETs) has been developed. The technique involves modification of NGSPICE, which is an open-source version of the popular Simulation Program with Integrated Circuit Emphasis (SPICE) general-purpose analog-integrated-circuit-simulating software. NGSPICE in its unmodified form is used for simulating and designing circuits made from silicon-based transistors that operate at or near room temperature. Two rapid modifications of NGSPICE source code enable SiC JFETs to be simulated to 500 C using the well-known Level 1 model for silicon metal oxide semiconductor field-effect transistors (MOSFETs). First, the default value of the MOSFET surface potential must be changed. In the unmodified source code, this parameter has a value of 0.6, which corresponds to slightly more than half the bandgap of silicon. In NGSPICE modified to simulate SiC JFETs, this parameter is changed to a value of 1.6, corresponding to slightly more than half the bandgap of SiC. The second modification consists of changing the temperature dependence of MOSFET transconductance and saturation parameters. The unmodified NGSPICE source code implements a T(sup -1.5) temperature dependence for these parameters. In order to mimic the temperature behavior of experimental SiC JFETs, a T(sup -1.3) temperature dependence must be implemented in the NGSPICE source code. Following these two simple modifications, the Level 1 MOSFET model of the NGSPICE circuit simulation program reasonably approximates the measured high-temperature behavior of experimental SiC JFETs properly operated with zero or reverse bias applied to the gate terminal. Modification of additional silicon parameters in the NGSPICE source code was not necessary to model experimental SiC JFET current-voltage performance across the entire temperature range from 25 to 500 C.

Effect of Cr, Ti, V, and Zr Micro-additions on Microstructure and Mechanical Properties of the Al-Si-Cu-Mg Cast Alloy

NASA Astrophysics Data System (ADS)

Shaha, S. K.; Czerwinski, F.; Kasprzak, W.; Friedman, J.; Chen, D. L.

2016-05-01

Uniaxial static and cyclic tests were used to assess the role of Cr, Ti, V, and Zr additions on properties of the Al-7Si-1Cu-0.5Mg (wt pct) alloy in as-cast and T6 heat-treated conditions. The microstructure of the as-cast alloy consisted of α-Al, eutectic Si, and Cu-, Mg-, and Fe-rich phases Al2.1Cu, Al8.5Si2.4Cu, Al5.2CuMg4Si5.1, and Al14Si7.1FeMg3.3. In addition, the micro-sized Cr/Zr/Ti/V-rich phases Al10.7SiTi3.6, Al6.7Si1.2TiZr1.8, Al21.4Si3.4Ti4.7VZr1.8, Al18.5Si7.3Cr2.6V, Al7.9Si8.5Cr6.8V4.1Ti, Al6.3Si23.2FeCr9.2V1.6Ti1.3, Al92.2Si16.7Fe7.6Cr8.3V1.8, and Al8.2Si30.1Fe1.6Cr18.8V3.3Ti2.9Zr were present. During solution treatment, Cu-rich phases were completely dissolved, while the eutectic silicon, Fe-, and Cr/Zr/Ti/V-rich intermetallics experienced only partial dissolution. Micro-additions of Cr, Zr, Ti, and V positively affected the alloy strength. The modified alloy in the T6 temper during uniaxial tensile tests exhibited yield strength of 289 MPa and ultimate tensile strength of 342 MPa, being significantly higher than that for the Al-Si-Cu-Mg base. Besides, the cyclic yield stress of the modified alloy in the T6 state increased by 23 pct over that of the base alloy. The fatigue life of the modified alloy was substantially longer than that of the base alloy tested using the same parameters. The role of Cr, Ti, V, and Zr containing phases in controlling the alloy fracture during static and cyclic loading is discussed.

Tribological properties of SiC-based MCD films synthesized using different carbon sources when sliding against Si3N4

NASA Astrophysics Data System (ADS)

Wang, Xinchang; Shen, Xiaotian; Zhao, Tianqi; Sun, Fanghong; Shen, Bin

2016-04-01

Micro-crystalline diamond (MCD) films are deposited on reactive sintering SiC substrates by the bias enhanced hot filament chemical vapor deposition (BE-HFCVD) method, respectively using the methane, acetone, methanol and ethanol as the carbon source. Two sets of standard tribotests are conducted, adopting Si3N4 balls as the counterpart balls, respectively with the purpose of clarifying differences among tribological properties of different MCD films, and studying detailed effects of the carbon source C, normal load Fn and sliding velocity v based on orthogonal analyses. It is clarified that the methane-MCD film presents the lowest growth rate, the highest film quality, the highest hardness and the best adhesion, in consequence, it also performs the best tribological properties, including the lowest coefficient of friction (COF) and wear rate Id, while the opposite is the methanol-MCD film. Under a normal load Fn of 7 N and at a sliding velocity v of 0.4183 m/s, for the methane-MCD film, the maximum COF (MCOF) is 0.524, the average COF during the relatively steady-state regime (ACOF) is 0.144, and the Id is about 1.016 × 10-7 mm3/N m; and for the methanol-MCD film, the MCOF is 0.667, the ACOF is 0.151, and the Id is 1.448 × 10-7 mm3/N m. Moreover, the MCOF, ACOF, Id and the wear rate of the Si3N4 ball Ib will all increase with the Fn, while the v only has significant effect on the ACOF, which shows a monotone increasing trend with the v.

Additive Effects on Si3n4 Oxidation/Volatilization in Water Vapor

NASA Technical Reports Server (NTRS)

Opila, Elizabeth J.; Robinson, R. Craig; Fox, Dennis S.; Wenglarz, Richard A.; Ferber, Mattison K.

2002-01-01

Two commercially available additive-containing silicon nitride materials were exposed in four environments which range in severity from dry oxygen at 1 atm pressure, and low gas velocity to an actual turbine engine. Oxidation and volatilization kinetics were monitored at temperatures ranging from 1066 to 1400 C. The main purpose of this paper is to examine the surface oxide morphology resulting from the exposures. It was found that the material surface was enriched in rare earth silicate phases in combustion environments when compared to the oxides formed on materials exposed in dry oxygen. However, the in situ formation of rare earth disilicate phases offered little additional protection from the volatilization of silica observed in combustion environments. It was concluded that externally applied environmental barrier coatings are needed to protect additive-containing silicon nitride materials from volatilization reactions in combustion environments. Introduction Si3N4 is proposed for use as components, such as vanes, in turbine applications. Tens of thousands of hours of life are needed for both land-based turbines and aeropropulsion applications. Additive-containing SisN4 materials are

Si1-yGey or Ge1-zSnz Source/Drain Stressors on Strained Si1-xGex-Channel P-Type Field-Effect Transistors: A Technology Computer-Aided Design Study

NASA Astrophysics Data System (ADS)

Eneman, Geert; De Keersgieter, An; Witters, Liesbeth; Mitard, Jerome; Vincent, Benjamin; Hikavyy, Andriy; Loo, Roger; Horiguchi, Naoto; Collaert, Nadine; Thean, Aaron

2013-04-01

The interaction between two stress techniques, strain-relaxed buffers (SRBs) and epitaxial source/drain stressors, is studied on short, Si1-xGex- and Ge-channel planar transistors. This work focuses on the longitudinal channel stress generated by these two techniques. Unlike for unstrained silicon-channel transistors, for strained channels on top of a strain-relaxed buffer a source/drain stressor without recess generates similar longitudinal channel stress than source/drain stressors with a deep recess. The least efficient stress transfer is obtained for source/drain stressors with a small recess that removes only the strained channel, not the substrate underneath. These trends are explained by a trade-off between elastic relaxation of the strained-channel during source/drain recess and the increased stress generation of thicker source/drain stressors. For Ge-channel pFETs, GeSn source/drains and Si1-xGex strain-relaxed buffers are efficient stressors for mobility enhancement. The former is more efficient for gate-last schemes than for gate-first, while the stress generated by the SRB is found to be independent of the gate-scheme.

Improving High-Temperature Tensile and Low-Cycle Fatigue Behavior of Al-Si-Cu-Mg Alloys Through Micro-additions of Ti, V, and Zr

NASA Astrophysics Data System (ADS)

Shaha, S. K.; Czerwinski, F.; Kasprzak, W.; Friedman, J.; Chen, D. L.

2015-07-01

High-temperature tensile and low-cycle fatigue tests were performed to assess the influence of micro-additions of Ti, V, and Zr on the improvement of the Al-7Si-1Cu-0.5Mg (wt pct) alloy in the as-cast condition. Addition of transition metals led to modification of microstructure where in addition to conventional phases present in the Al-7Si-1Cu-0.5Mg base, new thermally stable micro-sized Zr-Ti-V-rich phases Al21.4Si4.1Ti3.5VZr3.9, Al6.7Si1.2TiZr1.8, Al2.8Si3.8V1.6Zr, and Al5.1Si35.4Ti1.6Zr5.7Fe were formed. The tensile tests showed that with increasing test temperature from 298 K to 673 K (25 °C to 400 °C), the yield stress and tensile strength of the present studied alloy decreased from 161 to 84 MPa and from 261 to 102 MPa, respectively. Also, the studied alloy exhibited 18, 12, and 5 pct higher tensile strength than the alloy A356, 354 and existing Al-Si-Cu-Mg alloy modified with additions of Zr, Ti, and Ni, respectively. The fatigue life of the studied alloy was substantially longer than those of the reference alloys A356 and the same Al-7Si-1Cu-0.5Mg base with minor additions of V, Zr, and Ti in the T6 condition. Fractographic analysis after tensile tests revealed that at the lower temperature up to 473 K (200 °C), the cleavage-type brittle fracture for the precipitates and ductile fracture for the matrix were dominant while at higher temperature fully ductile-type fracture with debonding and pull-out of cracked particles was identified. It is believed that the intermetallic precipitates containing Zr, Ti, and V improve the alloy performance at increased temperatures.

Oxidation of TaSi2-Containing ZrB2-SiC Ultra-High Temperature Materials

NASA Technical Reports Server (NTRS)

Opila, Elizabeth J.; Smith, Jim; Levine, Stanley R.; Lorincz, Jonathan; Reigel, Marissa

2010-01-01

Hot pressed coupons of composition ZrB2-20 v% SiC-5 v% TaSi2 and ZrB2-20 v% SiC-20 v% TaSi2 were oxidized in stagnant air at temperatures of 1627 and 1927C for one, five and ten 10-minute cycles. The oxidation reactions were characterized by weight change kinetics, x-ray diffraction, and SEM/EDS. Detailed WDS/microprobe quantitative analyses of the oxidation products were conducted for the ZrB2-20 v% SiC-20 v% TaSi2 sample oxidized for five 10-minute cycles at 1927C. Oxidation kinetics and product formation were compared to ZrB2-20 v% SiC with no TaSi2 additions. It was found that the 20 v% TaSi2 composition exhibited improved oxidation resistance relative to the material with no TaSi2 additions at 1627C. However, for exposures at 1927C less oxidation resistance and extensive liquid phase formation were observed compared to the material with no TaSi2 additions. Attempts to limit the liquid phase formation by reducing the TaSi2 content to 5 v% were unsuccessful. In addition, the enhanced oxidation resistance at 1627C due to 20 v% TaSi2 additions was not achieved at the 5 v% addition level. The observed oxidation product evolution is discussed in terms of thermodynamics and phase equilibria for the TaSi2-containing ZrB2-SiC material system. TaSi2-additions to ZrB2-SiC at any level are not recommended for ultra-high temperature (>1900C) applications due to excessive liquid phase formation.

On-site SiH4 generator using hydrogen plasma generated in slit-type narrow gap

NASA Astrophysics Data System (ADS)

Takei, Norihisa; Shinoda, Fumiya; Kakiuchi, Hiroaki; Yasutake, Kiyoshi; Ohmi, Hiromasa

2018-06-01

We have been developing an on-site silane (SiH4) generator based on use of the chemical etching reaction between solid silicon (Si) and the high-density H atoms that are generated in high-pressure H2 plasma. In this study, we have developed a slit-type plasma source for high-efficiency SiH4 generation. High-density H2 plasma was generated in a narrow slit-type discharge gap using a 2.45 GHz microwave power supply. The plasma’s optical emission intensity distribution along the slit was measured and the resulting distribution was reflected by both the electric power distribution and the hydrogen gas flow. Because the Si etching rate strongly affects the SiH4 generation rate, the Si etching behavior was investigated with respect to variations in the experimental parameters. The weight etch rate increased monotonically with increasing input microwave power. However, the weight etch rate decreased with increasing H2 pressure and an increasing plasma gap. This reduction in the etch rate appears to be related to shrinkage of the plasma generation area because increased input power is required to maintain a constant plasma area with increasing H2 pressure and the increasing plasma gap. Additionally, the weight etch rate also increases with increasing H2 flow rate. The SiH4 generation rate of the slit-type plasma source was also evaluated using gas-phase Fourier transform infrared absorption spectroscopy and the material utilization efficiencies of both Si and the H2 gas for SiH4 gas formation were discussed. The main etch product was determined to be SiH4 and the developed plasma source achieved a SiH4 generation rate of 10 sccm (standard cubic centimeters per minute) at an input power of 900 W. In addition, the Si utilization efficiency exceeded 60%.

Single-source-precursor synthesis of dense SiC/HfCxN1-x-based ultrahigh-temperature ceramic nanocomposites

NASA Astrophysics Data System (ADS)

Wen, Qingbo; Xu, Yeping; Xu, Binbin; Fasel, Claudia; Guillon, Olivier; Buntkowsky, Gerd; Yu, Zhaoju; Riedel, Ralf; Ionescu, Emanuel

2014-10-01

A novel single-source precursor was synthesized by the reaction of an allyl hydrido polycarbosilane (SMP10) and tetrakis(dimethylamido)hafnium(iv) (TDMAH) for the purpose of preparing dense monolithic SiC/HfCxN1-x-based ultrahigh temperature ceramic nanocomposites. The materials obtained at different stages of the synthesis process were characterized via Fourier transform infrared (FT-IR) as well as nuclear magnetic resonance (NMR) spectroscopy. The polymer-to-ceramic transformation was investigated by means of MAS NMR and FT-IR spectroscopy as well as thermogravimetric analysis (TGA) coupled with in situ mass spectrometry. Moreover, the microstructural evolution of the synthesized SiHfCN-based ceramics annealed at different temperatures ranging from 1300 °C to 1800 °C was characterized by elemental analysis, X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM). Based on its high temperature behavior, the amorphous SiHfCN-based ceramic powder was used to prepare monolithic SiC/HfCxN1-x-based nanocomposites using the spark plasma sintering (SPS) technique. The results showed that dense monolithic SiC/HfCxN1-x-based nanocomposites with low open porosity (0.74 vol%) can be prepared successfully from single-source precursors. The average grain size of both HfC0.83N0.17 and SiC phases was found to be less than 100 nm after SPS processing owing to a unique microstructure: HfC0.83N0.17 grains were embedded homogeneously in a β-SiC matrix and encapsulated by in situ formed carbon layers which acted as a diffusion barrier to suppress grain growth. The segregated Hf-carbonitride grains significantly influenced the electrical conductivity of the SPS processed monolithic samples. While Hf-free polymer-derived SiC showed an electrical conductivity of ca. 1.8 S cm-1, the electrical conductivity of the Hf-containing material was analyzed to be ca. 136.2 S cm-1.A novel single-source precursor was synthesized by the reaction of an allyl hydrido

Effect of the addition of SF6 and N2 in inductively coupled SiCl4 plasma for GaN etching

NASA Astrophysics Data System (ADS)

Oubensaid, E. H.; Duluard, C. Y.; Pichon, L. E.; Pereira, J.; Boufnichel, M.; Lefaucheux, P.; Dussart, R.; Ranson, P.

2009-07-01

The GaN etching by SiCl4 plasma is considered in an ICP tool. By respecting some material limitations, it has been possible to etch the gallium nitride in pure SiCl4 plasma, with an etch rate of 19 nm min-1. This result is comparable to other reported results. Thereafter, the combination of SiCl4 with SF6 and N2 was tested in order to increase the etch rate. The addition of SF6 in the plasma has enabled us to reach an etch rate of 53 nm min-1. However, best results were obtained with the addition of N2, with an increase of the etch rate by a factor of 6. Mass spectrometry was also performed in order to determine the effects of the additional gases. The surface morphology of the GaN was also analysed by scanning electron microscope after etching.

Reducing contralateral SI activity reveals hindlimb receptive fields in the SI forelimb-stump representation of neonatally amputated rats.

PubMed

Pluto, Charles P; Chiaia, Nicolas L; Rhoades, Robert W; Lane, Richard D

2005-09-01

In adult rats that sustained forelimb amputation on the day of birth, >30% of multiunit recording sites in the forelimb-stump representation of primary somatosensory cortex (SI) also respond to cutaneous hindlimb stimulation when cortical GABA(A+B) receptors are blocked (GRB). This study examined whether hindlimb receptive fields could also be revealed in forelimb-stump sites by reducing one known source of excitatory input to SI GABAergic neurons, the contralateral SI cortex. Corpus callosum projection neurons connect homotopic SI regions, making excitatory contacts onto pyramidal cells and interneurons. Thus in addition to providing monosynaptic excitation in SI, callosal fibers can produce disynaptic inhibition through excitatory synapses with inhibitory interneurons. Based on the latter of these connections, we hypothesized that inactivating the contralateral (intact) SI forelimb region would "unmask" normally suppressed hindlimb responses by reducing the activity of SI GABAergic neurons. The SI forelimb-stump representation was first mapped under normal conditions and then during GRB to identify stump/hindlimb responsive sites. After GRB had dissipated, the contralateral (intact) SI forelimb region was mapped and reversibly inactivated with injections of 4% lidocaine, and selected forelimb-stump sites were retested. Contralateral SI inactivation revealed hindlimb responses in approximately 60% of sites that were stump/hindlimb responsive during GRB. These findings indicate that activity in the contralateral SI contributes to the suppression of reorganized hindlimb receptive fields in neonatally amputated rats.

Comparison of low frequency charge noise in identically patterned Si/SiO{sub 2} and Si/SiGe quantum dots

DOE Office of Scientific and Technical Information (OSTI.GOV)

Freeman, Blake M.; Schoenfield, Joshua S.; Jiang, HongWen

We investigate and compare the charge noise in Si/SiO{sub 2} and Si/SiGe gate defined quantum dots with identically patterned gates by measuring the low frequency 1/f current noise through the biased quantum dots in the coulomb blockade regime. The current noise is normalized and used to extract a measurement of the potential energy noise in the system. Additionally, the temperature dependence of this noise is investigated. The measured charge noise in Si/SiO{sub 2} compares favorably with that of the SiGe device as well as previous measurements made on other substrates suggesting Si/SiO{sub 2} is a potential candidate for spin basedmore » quantum computing.« less

Stress engineering in GaN structures grown on Si(111) substrates by SiN masking layer application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szymański, Tomasz, E-mail: tomasz.szymanski@pwr.edu.pl; Wośko, Mateusz; Paszkiewicz, Bogdan

2015-07-15

GaN layers without and with an in-situ SiN mask were grown by using metal organic vapor phase epitaxy for three different approaches used in GaN on silicon(111) growth, and the physical and optical properties of the GaN layers were studied. For each approach applied, GaN layers of 1.4 μm total thickness were grown, using silan SiH{sub 4} as Si source in order to grow Si{sub x}N{sub x} masking layer. The optical micrographs, scanning electron microscope images, and atomic force microscope images of the grown samples revealed cracks for samples without SiN mask, and micropits, which were characteristic for the samples grownmore » with SiN mask. In situ reflectance signal traces were studied showing a decrease of layer coalescence time and higher degree of 3D growth mode for samples with SiN masking layer. Stress measurements were conducted by two methods—by recording micro-Raman spectra and ex-situ curvature radius measurement—additionally PLs spectra were obtained revealing blueshift of PL peak positions with increasing stress. The authors have shown that a SiN mask significantly improves physical and optical properties of GaN multilayer systems reducing stress in comparison to samples grown applying the same approaches but without SiN masking layer.« less

Challenge of Si/SiGe technology to optoelectronics

NASA Astrophysics Data System (ADS)

Chang, C. Y.; Jung, J. G.

1993-01-01

Low temperature epitaxy (LTE) of Si and SiGecanbe performed at a temperature of 550 C or lower. Very promising applications can be opened. Such as high speed/high frequency operations at 90GHZ by constructing heterojunction bipolar transistors. High performance FET'slikepseudomorphic p-channel orn-channel high mobility field effect transistors are presented which canbe composed to perform CMOS operations. Optoelectronic devices such as IRdetectors (1-12um), mutiple quantum well (MOW), disordered superlattice (d-SL) which are the potential candidatesof IR detector and optical sources (e.q. LED, LD etc.) Various physical insights regarding to SiGe heterostructures are presented which includeswave function filter, mass filter as well as band mixing are introduced. Researchesat National Nano Device Laboratory (NDL) which processes the capability of 0.3um Si ULSI technologies and SiGe works as well as lll-V, a-Si/SiGe lines are also presented.

5 CFR 3601.103 - Additional exceptions for gifts from outside sources.

Code of Federal Regulations, 2010 CFR

2010-01-01

... 5 Administrative Personnel 3 2010-01-01 2010-01-01 false Additional exceptions for gifts from... gifts from outside sources. In addition to the gifts which come within the exceptions set forth in 5 CFR... gifts from outside sources otherwise prohibited by 5 CFR 2635.202(a) as follows: (a) Events sponsored by...

Microprocessing of ITO and a-Si thin films using ns laser sources

NASA Astrophysics Data System (ADS)

Molpeceres, C.; Lauzurica, S.; Ocaña, J. L.; Gandía, J. J.; Urbina, L.; Cárabe, J.

2005-06-01

Selective ablation of thin films for the development of new photovoltaic panels and sensoring devices based on amorphous silicon (a-Si) is an emerging field, in which laser micromachining systems appear as appropriate tools for process development and device fabrication. In particular, a promising application is the development of purely photovoltaic position sensors. Standard p-i-n or Schottky configurations using transparent conductive oxides (TCO), a-Si and metals are especially well suited for these applications, appearing selective laser ablation as an ideal process for controlled material patterning and isolation. In this work a detailed study of laser ablation of a widely used TCO, indium-tin-oxide (ITO), and a-Si thin films of different thicknesses is presented, with special emphasis on the morphological analysis of the generated grooves. Excimer (KrF, λ = 248 nm) and DPSS lasers (λ = 355 and λ = 1064 nm) with nanosecond pulse duration have been used for material patterning. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) techniques have been applied for the characterization of the ablated grooves. Additionally, process parametric windows have been determined in order to assess this technology as potentially competitive to standard photolithographic processes. The encouraging results obtained, with well-defined ablation grooves having thicknesses in the order of 10 µm both in ITO and in a-Si, open up the possibility of developing a high-performance double Schottky photovoltaic matrix position sensor.

Si light-emitting device in integrated photonic CMOS ICs

NASA Astrophysics Data System (ADS)

Xu, Kaikai; Snyman, Lukas W.; Aharoni, Herzl

2017-07-01

The motivation for integrated Si optoelectronics is the creation of low-cost photonics for mass-market applications. Especially, the growing demand for sensitive biochemical sensors in the environmental control or medicine leads to the development of integrated high resolution sensors. Here CMOS-compatible Si light-emitting device structures are presented for investigating the effect of various depletion layer profiles and defect engineering on the photonic transition in the 1.4-2.8 eV. A novel Si device is proposed to realize both a two-terminal Si-diode light-emitting device and a three-terminal Si gate-controlled diode light-emitting device in the same device structure. In addition to the spectral analysis, differences between two-terminal and three-terminal devices are discussed, showing the light emission efficiency change. The proposed Si optical source may find potential applications in micro-photonic systems and micro-optoelectro-mechanical systems (MOEMS) in CMOS integrated circuitry.

Addition of poly (propylene glycol) to multiblock copolymer to optimize siRNA delivery.

PubMed

Dai, Zhi; Arévalo, Maria T; Li, Junwei; Zeng, Mingtao

2014-01-01

Previous studies have examined different strategies for siRNA delivery with varying degrees of success. These include use of viral vectors, cationic liposomes, and polymers. Several copolymers were designed and synthesized based on blocks of poly(ethylene glycol) PEG, poly(propylene glycol) PPG, and poly(l-lysine). These were designated as P1, P2, and P3. We studied the copolymer self-assembly, siRNA binding, particle size, surface potential, architecture of the complexes, and siRNA delivery. Silencing of GFP using copolymer P3 to deliver GFP-specific siRNA to Neuro-2a cells expressing GFP was almost as effective as using Lipofectamine 2000, with minimal cytotoxicity. Thus, we have provided a new copolymer platform for siRNA delivery that we can continue to modify for improved delivery of siRNA in vitro and eventually in vivo.

Consolidation of Si3N4 without additives (by hot isostatic pressing)

NASA Technical Reports Server (NTRS)

Yeh, H. C.

1983-01-01

The potential of using hot isostatic pressing (HIP'ing) technique to produce dense silicon nitride materials without or with a reduced amount of additives (much less than 5 w/o) was investigated. Hot isostatic pressing technique can provide higher pressure and temperature than hot pressing can, thus has the potential of requiring less densification aids to consolidate Si3N4 materials. It was anticipated that if such dense materials could be fabricated, the high temperature strength of the material should be improved significantly. Observations on the phase transformation, densification behavior, and microstructures of the samples are also documented. Density, microhardness, four point bend strength (room temperature and 1370 C) were measured on selected densified materials.

Effect of Al-TiB Addition on the Mechanical Properties and Microstructure of Al-ADC12/NanoSiC Produced by Stir Casting Methods

NASA Astrophysics Data System (ADS)

Dhaneswara, D.; Zulfia, A.; Pramudita, T. P.; Ferdian, D.; Utomo, B. W.

2018-03-01

Addition of Ti-B grain refiner in Al-ADC12/nanoSiC composite results in improvement of tensile strength, hardness, and wear resistance through grain refinement. In this research, composite of Al-ADC12/nano SiC (0.15 %vf) with variations of TiB respectively (0.0), (0.02), (0.04), (0.06), dan (0.08) wt% were produced by stir casting. 10% of Mg were added to promote wettability between reinforce and matrix. It was found the best addition of TiB is 0.04 wt% Ti-B which results 135,9 MPa in tensile strength, 46 HRB in hardness, and 1.47x10-5 mm3/s as wear rate. The increase in mechanical properties of composites mainly because of Al3Ti acts as nucleants which initiates the grain refinement and the existence of MgAl2O4 phase indicates an interphase between nano SiC and ADC12 matrix. However, the increase of Ti-B addition after optimum number gives no significant results. High composition of iron and magnesium addition will form intermetallic phase β-Fe, π-Fe, and Mg2Si.

Mechanism for Si-Si Bond Rupture in Single Molecule Junctions.

PubMed

Li, Haixing; Kim, Nathaniel T; Su, Timothy A; Steigerwald, Michael L; Nuckolls, Colin; Darancet, Pierre; Leighton, James L; Venkataraman, Latha

2016-12-14

The stability of chemical bonds can be studied experimentally by rupturing single molecule junctions under applied voltage. Here, we compare voltage-induced bond rupture in two Si-Si backbones: one has no alternate conductive pathway whereas the other contains an additional naphthyl pathway in parallel to the Si-Si bond. We show that in contrast to the first system, the second can conduct through the naphthyl group when the Si-Si bond is ruptured using an applied voltage. We investigate this voltage induced Si-Si bond rupture by ab initio density functional theory calculations and molecular dynamics simulations that ultimately demonstrate that the excitation of molecular vibrational modes by tunneling electrons leads to homolytic Si-Si bond rupture.

Single-source-precursor synthesis of dense SiC/HfC(x)N(1-x)-based ultrahigh-temperature ceramic nanocomposites.

PubMed

Wen, Qingbo; Xu, Yeping; Xu, Binbin; Fasel, Claudia; Guillon, Olivier; Buntkowsky, Gerd; Yu, Zhaoju; Riedel, Ralf; Ionescu, Emanuel

2014-11-21

A novel single-source precursor was synthesized by the reaction of an allyl hydrido polycarbosilane (SMP10) and tetrakis(dimethylamido)hafnium(iv) (TDMAH) for the purpose of preparing dense monolithic SiC/HfC(x)N(1-x)-based ultrahigh temperature ceramic nanocomposites. The materials obtained at different stages of the synthesis process were characterized via Fourier transform infrared (FT-IR) as well as nuclear magnetic resonance (NMR) spectroscopy. The polymer-to-ceramic transformation was investigated by means of MAS NMR and FT-IR spectroscopy as well as thermogravimetric analysis (TGA) coupled with in situ mass spectrometry. Moreover, the microstructural evolution of the synthesized SiHfCN-based ceramics annealed at different temperatures ranging from 1300 °C to 1800 °C was characterized by elemental analysis, X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM). Based on its high temperature behavior, the amorphous SiHfCN-based ceramic powder was used to prepare monolithic SiC/HfC(x)N(1-x)-based nanocomposites using the spark plasma sintering (SPS) technique. The results showed that dense monolithic SiC/HfC(x)N(1-x)-based nanocomposites with low open porosity (0.74 vol%) can be prepared successfully from single-source precursors. The average grain size of both HfC0.83N0.17 and SiC phases was found to be less than 100 nm after SPS processing owing to a unique microstructure: HfC0.83N0.17 grains were embedded homogeneously in a β-SiC matrix and encapsulated by in situ formed carbon layers which acted as a diffusion barrier to suppress grain growth. The segregated Hf-carbonitride grains significantly influenced the electrical conductivity of the SPS processed monolithic samples. While Hf-free polymer-derived SiC showed an electrical conductivity of ca. 1.8 S cm(-1), the electrical conductivity of the Hf-containing material was analyzed to be ca. 136.2 S cm(-1).

Etching characteristics of Si{110} in 20 wt% KOH with addition of hydroxylamine for the fabrication of bulk micromachined MEMS

NASA Astrophysics Data System (ADS)

Rao, A. V. Narasimha; Swarnalatha, V.; Pal, P.

2017-12-01

Anisotropic wet etching is a most widely employed for the fabrication of MEMS/NEMS structures using silicon bulk micromachining. The use of Si{110} in MEMS is inevitable when a microstructure with vertical sidewall is to be fabricated using wet anisotropic etching. In most commonly employed etchants (i.e. TMAH and KOH), potassium hydroxide (KOH) exhibits higher etch rate and provides improved anisotropy between Si{111} and Si{110} planes. In the manufacturing company, high etch rate is demanded to increase the productivity that eventually reduces the cost of end product. In order to modify the etching characteristics of KOH for the micromachining of Si{110}, we have investigated the effect of hydroxylamine (NH2OH) in 20 wt% KOH solution. The concentration of NH2OH is varied from 0 to 20% and the etching is carried out at 75 °C. The etching characteristics which are studied in this work includes the etch rates of Si{110} and silicon dioxide, etched surface morphology, and undercutting at convex corners. The etch rate of Si{110} in 20 wt% KOH + 15% NH2OH solution is measured to be four times more than that of pure 20 wt% KOH. Moreover, the addition of NH2OH increases the undercutting at convex corners and enhances the etch selectivity between Si and SiO2.

a-Si:H/SiNW shell/core for SiNW solar cell applications

PubMed Central

2013-01-01

Vertically aligned silicon nanowires have been synthesized by the chemical etching of silicon wafers. The influence of a hydrogenated amorphous silicon (a-Si:H) layer (shell) on top of a silicon nanowire (SiNW) solar cell has been investigated. The optical properties of a-Si:H/SiNWs and SiNWs are examined in terms of optical reflection and absorption properties. In the presence of the a-Si:H shell, 5.2% reflection ratio in the spectral range (250 to 1,000 nm) is achieved with a superior absorption property with an average over 87% of the incident light. In addition, the characteristics of the solar cell have been significantly improved, which exhibits higher open-circuit voltage, short-circuit current, and efficiency by more than 15%, 12%, and 37%, respectively, compared with planar SiNW solar cells. Based on the current–voltage measurements and morphology results, we show that the a-Si:H shell can passivate the defects generated by wet etching processes. PMID:24195734

Modifying Si-based consolidants through the addition of colloidal nano-particles

NASA Astrophysics Data System (ADS)

Ksinopoulou, E.; Bakolas, A.; Moropoulou, A.

2016-04-01

The modification of silicon-based stone consolidants has been the subject of many scientific studies aiming to overcome the commonly reported drawbacks of these materials, such as the tendency to shrink and crack during drying. The addition of nano-particle dispersions into silica matrix has been found to enhance their effectiveness in several ways. Objective of the current research was to study the preparation of particle-modified consolidants (PMC), consisting of an ethyl silicate matrix (TEOS) loaded with colloidal silica (SiO2) nano-particles and oxide titania (TiO2) particles. The effect of the polyacrylic acid on the dispersion stability was also investigated, by varying its concentration into PMC samples. The prepared materials were allowed to dry in two different relative humidity environments and then evaluated based on their stability in the sol phase, the aggregation sizes, determined through dynamic light scattering, the % solids content and their morphological characteristics, observed via scanning electron microscopy (SEM-EDAX). Mercury intrusion porosimetry was also applied to investigate the microstructural characteristics and differences between the prepared consolidants. Significant role in the final form of the material is played by both the initial molar ratios in the mixtures, as well as the conditions where the drying and aging takes place. Based on the results, the three-component PMCs appear to be promising in stone consolidation, as they show a reduction in cracking and shrinkage during drying and a more porous network, compared with the siliceous material, or the two-component TEOS-SiO2 formulation.

Optimization of heat treatment parameters for additive manufacturing and gravity casting AlSi10Mg alloy

NASA Astrophysics Data System (ADS)

Girelli, L.; Tocci, M.; Montesano, L.; Gelfi, M.; Pola, A.

2017-11-01

Additive manufacturing of metals is a production process developed in the last few years to realize net shape components with complex geometry and high performance. AlSi10Mg is one of the most widely used aluminium alloys, both in this field and in conventional foundry processes, for its significant mechanical properties combined with good corrosion resistance. In this paper the effect of heat treatment on AlSi10Mg alloy was investigated. Solution and ageing treatments were carried out with different temperatures and times on samples obtained by direct metal laser sintering and gravity casting in order to compare their performance. Microstructural analyses and hardness tests were performed to investigate the effectiveness of the heat treatment. The results were correlated to the sample microstructure and porosity, analysed by means of optical microscopy and density measurements. It was found that, in the additive manufactured samples, the heat treatment can reduce significantly the performance of the alloy also because of the increase of porosity due to entrapped gas during the deposition technique and that the higher the solution temperature the higher the increase of such defects. A so remarkable effect was not found in the conventional cast alloy.

Construction and characterization of spherical Si solar cells combined with SiC electric power inverter

NASA Astrophysics Data System (ADS)

Oku, Takeo; Matsumoto, Taisuke; Hiramatsu, Kouichi; Yasuda, Masashi; Shimono, Akio; Takeda, Yoshikazu; Murozono, Mikio

2015-02-01

Spherical silicon (Si) photovoltaic solar cell systems combined with an electric power inverter using silicon carbide (SiC) field-effect transistor (FET) were constructed and characterized, which were compared with an ordinary Si-based converter. The SiC-FET devices were introduced in the direct current-alternating current (DC-AC) converter, which was connected with the solar panels. The spherical Si solar cells were used as the power sources, and the spherical Si panels are lighter and more flexible compared with the ordinary flat Si solar panels. Conversion efficiencies of the spherical Si solar cells were improved by using the SiC-FET.

SiC Nanoparticles Toughened-SiC/MoSi2-SiC Multilayer Functionally Graded Oxidation Protective Coating for Carbon Materials at High Temperatures

NASA Astrophysics Data System (ADS)

Abdollahi, Alireza; Ehsani, Naser; Valefi, Zia; Khalifesoltani, Ali

2017-05-01

A SiC nanoparticle toughened-SiC/MoSi2-SiC functionally graded oxidation protective coating on graphite was prepared by reactive melt infiltration (RMI) at 1773 and 1873 K under argon atmosphere. The phase composition and anti-oxidation behavior of the coatings were investigated. The results show that the coating was composed of MoSi2, α-SiC and β-SiC. By the variations of Gibbs free energy (calculated by HSC Chemistry 6.0 software), it could be suggested that the SiC coating formed at low temperatures by solution-reprecipitation mechanism and at high temperatures by gas-phase reactions and solution-reprecipitation mechanisms simultaneously. SiC nanoparticles could improve the oxidation resistance of SiC/MoSi2-SiC multiphase coating. Addition of SiC nanoparticles increases toughness of the coating and prevents spreading of the oxygen diffusion channels in the coating during the oxidation test. The mass loss and oxidation rate of the SiC nanoparticle toughened-SiC/MoSi2-SiC-coated sample after 10-h oxidation at 1773 K were only 1.76% and 0.32 × 10-2 g/cm3/h, respectively.

Fast growth of n-type 4H-SiC bulk crystal by gas-source method

NASA Astrophysics Data System (ADS)

Hoshino, Norihiro; Kamata, Isaho; Tokuda, Yuichiro; Makino, Emi; Kanda, Takahiro; Sugiyama, Naohiro; Kuno, Hironari; Kojima, Jun; Tsuchida, Hidekazu

2017-11-01

Fast growth of n-type 4H-SiC crystals was attempted using a high-temperature gas-source method. High growth rates exceeding 9 mm/h were archived at a seed temperature of 2550 °C, although the formation of macro-step bunching caused doping fluctuation and voids in the grown crystal. We investigated a trade-off between growth-rate enhancement and macro-step formation and how to improve the trade-off. By controlling the growth conditions, the growth of highly nitrogen-doped 4H-SiC crystals without the doping fluctuation and void formation were accomplished under a high growth rate exceeding 3 mm/h, maintaining the density of threading screw dislocations in the same level with the seed crystal. The influence of growth parameters on nitrogen incorporations into grown crystals was also surveyed.

Characterization of Ultra High Temperature Ceramics via Transmission Electron Microscopy. Part 2: UHTCs sintered with addition of TaSi2

DTIC Science & Technology

2010-01-21

substituted by Hf in the TaSi2 phase, indicating that this silicide has a great solubility for the group IV metals . At the triple point junctions Ta5Si3...Mathis Müller for his precious help in TEM specimens’ preparations . FA8655-09-M-4002 40 References 1. L. E. Toth: Transition Metal Carbides and...Transition Metal Disilicides,’ Acta Mater., 44, 3035 (1996). 21. H. Pastor and R. Meyer: An Investigation of the Effect of Additions of Metal Silicides

Delayed plastic relaxation limit in SiGe islands grown by Ge diffusion from a local source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vanacore, G. M.; Zani, M.; Tagliaferri, A., E-mail: alberto.tagliaferri@polimi.it

2015-03-14

The hetero-epitaxial strain relaxation in nano-scale systems plays a fundamental role in shaping their properties. Here, the elastic and plastic relaxation of self-assembled SiGe islands grown by surface-thermal-diffusion from a local Ge solid source on Si(100) are studied by atomic force and transmission electron microscopies, enabling the simultaneous investigation of the strain relaxation in different dynamical regimes. Islands grown by this technique remain dislocation-free and preserve a structural coherence with the substrate for a base width as large as 350 nm. The results indicate that a delay of the plastic relaxation is promoted by an enhanced Si-Ge intermixing, induced by themore » surface-thermal-diffusion, which takes place already in the SiGe overlayer before the formation of a critical nucleus. The local entropy of mixing dominates, leading the system toward a thermodynamic equilibrium, where non-dislocated, shallow islands with a low residual stress are energetically stable. These findings elucidate the role of the interface dynamics in modulating the lattice distortion at the nano-scale, and highlight the potential use of our growth strategy to create composition and strain-controlled nano-structures for new-generation devices.« less

Abiologic silicon isotope fractionation between aqueous Si and Fe(III)-Si gel in simulated Archean seawater: Implications for Si isotope records in Precambrian sedimentary rocks

NASA Astrophysics Data System (ADS)

Zheng, Xin-Yuan; Beard, Brian L.; Reddy, Thiruchelvi R.; Roden, Eric E.; Johnson, Clark M.

2016-08-01

Precambrian Si-rich sedimentary rocks, including cherts and banded iron formations (BIFs), record a >7‰ spread in 30Si/28Si ratios (δ30Si values), yet interpretation of this large variability has been hindered by the paucity of data on Si isotope exchange kinetics and equilibrium fractionation factors in systems that are pertinent to Precambrian marine conditions. Using the three-isotope method and an enriched 29Si tracer, a series of experiments were conducted to constrain Si isotope exchange kinetics and fractionation factors between amorphous Fe(III)-Si gel, a likely precursor to Precambrian jaspers and BIFs, and aqueous Si in artificial Archean seawater under anoxic conditions. Experiments were conducted at room temperature, and in the presence and absence of aqueous Fe(II) (Fe(II)aq). Results of this study demonstrate that Si solubility is significantly lower for Fe-Si gel than that of amorphous Si, indicating that seawater Si concentrations in the Precambrian may have been lower than previous estimates. The experiments reached ∼70-90% Si isotope exchange after a period of 53-126 days, and the highest extents of exchange were obtained where Fe(II)aq was present, suggesting that Fe(II)-Fe(III) electron-transfer and atom-exchange reactions catalyze Si isotope exchange through breakage of Fe-Si bonds. All experiments except one showed little change in the instantaneous solid-aqueous Si isotope fractionation factor with time, allowing extraction of equilibrium Si isotope fractionation factors through extrapolation to 100% isotope exchange. The equilibrium 30Si/28Si fractionation between Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -2.30 ± 0.25‰ (2σ) in the absence of Fe(II)aq. In the case where Fe(II)aq was present, which resulted in addition of ∼10% Fe(II) in the final solid, creating a mixed Fe(II)-Fe(III) Si gel, the equilibrium fractionation between Fe(II)-Fe(III)-Si gel and aqueous Si (Δ30Sigel-aqueous) is -3.23 ± 0.37‰ (2�

Impact of SiNx capping on the formation of source/drain contact for In-Ga-Zn-O thin film transistor with self-aligned gate

NASA Astrophysics Data System (ADS)

Oh, Himchan; Pi, Jae-Eun; Hwang, Chi-Sun; Kwon, Oh-Sang

2017-12-01

Self-aligned gate structures are preferred for faster operation and scaling down of thin film transistors by reducing the overlapped region between source/drain and gate electrodes. Doping on source/drain regions is essential to fabricate such a self-aligned gate thin film transistor. For oxide semiconductors such as In-Ga-Zn-O, SiNx capping readily increases their carrier concentration. We report that the SiNx deposition temperature and thickness significantly affect the device properties, including threshold voltage, field effect mobility, and contact resistance. The reason for these variations in device characteristics mainly comes from the extension of the doped region to the gated area after the SiNx capping step. Analyses on capacitance-voltage and transfer length characteristics support this idea.

Hydrogen passivation of poly-Si/SiOx contacts for Si solar cells using Al2O3 studied with deuterium

NASA Astrophysics Data System (ADS)

Schnabel, Manuel; van de Loo, Bas W. H.; Nemeth, William; Macco, Bart; Stradins, Paul; Kessels, W. M. M.; Young, David L.

2018-05-01

The interplay between hydrogenation and passivation of poly-Si/SiOx contacts to n-type Si wafers is studied using atomic layer deposited Al2O3 and anneals in forming gas and nitrogen. The poly-Si/SiOx stacks are prepared by thermal oxidation followed by thermal crystallization of a-Si:H films deposited by plasma-enhanced chemical vapor deposition. Implied open-circuit voltages as high as 710 mV are achieved for p-type poly-Si/SiOx contacts to n-type Si after hydrogenation. Correlating minority carrier lifetime data and secondary ion mass spectrometry profiles reveals that the main benefit of Al2O3 is derived from its role as a hydrogen source for chemically passivating defects at SiOx; Al2O3 layers are found to hydrogenate poly-Si/SiOx much better than a forming gas anneal. By labelling Al2O3 and the subsequent anneal with different hydrogen isotopes, it is found that Al2O3 exchanges most of its hydrogen with the ambient upon annealing at 400 °C for 1 h even though there is no significant net change in its total hydrogen content.

36 CFR 1290.3 - Sources of assassination records and additional records and information.

Code of Federal Regulations, 2010 CFR

2010-07-01

... Sources of assassination records and additional records and information. Assassination records and... 36 Parks, Forests, and Public Property 3 2010-07-01 2010-07-01 false Sources of assassination records and additional records and information. 1290.3 Section 1290.3 Parks, Forests, and Public Property...

Uptake of Silicon by Sugarcane from Applied Sources May Not Reflect Plant-Available Soil Silicon and Total Silicon Content of Sources.

PubMed

Keeping, Malcolm G

2017-01-01

Soils of the tropics and sub-tropics are typically acid and depleted of soluble sources of silicon (Si) due to weathering and leaching associated with high rainfall and temperatures. Together with intensive cropping, this leads to marginal or deficient plant Si levels in Si-accumulating crops such as rice and sugarcane. Although such deficiencies can be corrected with exogenous application of Si sources, there is controversy over the effectiveness of sources in relation to their total Si content, and their capacity to raise soil and plant Si concentrations. This study tested the hypothesis that the total Si content and provision of plant-available Si from six sources directly affects subsequent plant Si uptake as reflected in leaf Si concentration. Two trials with potted cane plants were established with the following Si sources as treatments: calcium silicate slag, fused magnesium (thermo) phosphate, volcanic rock dust, magnesium silicate, and granular potassium silicate. Silicon sources were applied at rates intended to achieve equivalent elemental soil Si concentrations; controls were untreated or lime-treated. Analyses were conducted to determine soil and leaf elemental concentrations. Among the sources, calcium silicate produced the highest leaf Si concentrations, yet lower plant-available soil Si concentrations than the thermophosphate. The latter, with slightly higher total Si than the slag, produced substantially greater increases in soil Si than all other products, yet did not significantly raise leaf Si above the controls. All other sources did not significantly increase soil or leaf Si concentrations, despite their high Si content. Hence, the total Si content of sources does not necessarily concur with a product's provision of soluble soil Si and subsequent plant uptake. Furthermore, even where soil pH was raised, plant uptake from thermophosphate was well below expectation, possibly due to its limited liming capacity. The ability of the calcium silicate

Uptake of Silicon by Sugarcane from Applied Sources May Not Reflect Plant-Available Soil Silicon and Total Silicon Content of Sources

PubMed Central

Keeping, Malcolm G.

2017-01-01

Soils of the tropics and sub-tropics are typically acid and depleted of soluble sources of silicon (Si) due to weathering and leaching associated with high rainfall and temperatures. Together with intensive cropping, this leads to marginal or deficient plant Si levels in Si-accumulating crops such as rice and sugarcane. Although such deficiencies can be corrected with exogenous application of Si sources, there is controversy over the effectiveness of sources in relation to their total Si content, and their capacity to raise soil and plant Si concentrations. This study tested the hypothesis that the total Si content and provision of plant-available Si from six sources directly affects subsequent plant Si uptake as reflected in leaf Si concentration. Two trials with potted cane plants were established with the following Si sources as treatments: calcium silicate slag, fused magnesium (thermo) phosphate, volcanic rock dust, magnesium silicate, and granular potassium silicate. Silicon sources were applied at rates intended to achieve equivalent elemental soil Si concentrations; controls were untreated or lime-treated. Analyses were conducted to determine soil and leaf elemental concentrations. Among the sources, calcium silicate produced the highest leaf Si concentrations, yet lower plant-available soil Si concentrations than the thermophosphate. The latter, with slightly higher total Si than the slag, produced substantially greater increases in soil Si than all other products, yet did not significantly raise leaf Si above the controls. All other sources did not significantly increase soil or leaf Si concentrations, despite their high Si content. Hence, the total Si content of sources does not necessarily concur with a product's provision of soluble soil Si and subsequent plant uptake. Furthermore, even where soil pH was raised, plant uptake from thermophosphate was well below expectation, possibly due to its limited liming capacity. The ability of the calcium silicate

SI: The Stellar Imager

NASA Technical Reports Server (NTRS)

Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

2006-01-01

The ultra-sharp images of the Stellar Imager (SI) will revolutionize our view of many dynamic astrophysical processes: The 0.1 milliarcsec resolution of this deep-space telescope will transform point sources into extended sources, and simple snapshots into spellbinding evolving views. SI s science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI s prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era by imaging a sample of magnetically active stars with enough resolution to map their evolving dynamo patterns and their internal flows. By exploring the Universe at ultra-high resolution, SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled structures and processes in the Universe.

The Abundance of SiC2 in Carbon Star Envelopes: Evidence that SiC2 is a gas-phase precursor of SiC dust.

PubMed

Massalkhi, Sarah; Agúndez, M; Cernicharo, J; Velilla Prieto, L; Goicoechea, J R; Quintana-Lacaci, G; Fonfría, J P; Alcolea, J; Bujarrabal, V

2018-03-01

Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si-C bond detected in C-rich AGB stars are SiC 2 , SiC, and Si 2 C. To date, the ring molecule SiC 2 has been observed in a handful of evolved stars, while SiC and Si 2 C have only been detected in the C-star envelope IRC +10216. We aim to study how widespread and abundant SiC 2 , SiC, and Si 2 C are in envelopes around C-rich AGB stars and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars. We carried out sensitive observations with the IRAM 30m telescope of a sample of 25 C-rich AGB stars to search for emission lines of SiC 2 , SiC, and Si 2 C in the λ 2 mm band. We performed non-LTE excitation and radiative transfer calculations based on the LVG method to model the observed lines of SiC 2 and to derive SiC 2 fractional abundances in the observed envelopes. We detect SiC 2 in most of the sources, SiC in about half of them, and do not detect Si 2 C in any source, at the exception of IRC +10216. Most of these detections are reported for the first time in this work. We find a positive correlation between the SiC and SiC 2 line emission, which suggests that both species are chemically linked, the SiC radical probably being the photodissociation product of SiC 2 in the external layer of the envelope. We find a clear trend in which the denser the envelope, the less abundant SiC 2 is. The observed trend is interpreted as an evidence of efficient incorporation of SiC 2 onto dust grains, a process which is favored at high densities owing to the higher rate at which collisions between particles take place. The observed behavior of a decline in the SiC 2 abundance with increasing density strongly suggests that SiC 2 is an important gas

Effect of Cr and Mn addition and heat treatment on AlSi3Mg casting alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tocci, Marialaura, E-mail: m.tocci@unibs.it

In the present paper the effect of heat treatment on an AlSi3Mg alloy with and without Cr and Mn addition was investigated. Beside the well-known modification of the morphology of Fe-containing intermetallics, it was found that Cr and Mn allowed the formation of dispersoids in the aluminium matrix after solution heat treatment at 545 °C, as shown by scanning transmission electron microscope observations. These particles were responsible of the enhanced Vickers microhardness of the aluminium matrix in comparison with the base alloy after solution treatment and quenching, according to dispersion hardening mechanism. The presence of these particles was not affectedmore » by ageing treatment, which instead allowed the precipitation of β-Mg{sub 2}Si, as shown by the elaboration of differential scanning calorimeter curves. The formation of dispersoids and the study of their effect on mechanical properties can represent an interesting development for applications at high temperatures of casting alloys due to their thermal stability compared to other strengthening phases as β-Mg{sub 2}Si. - Highlights: •Cr and Mn successfully modified the morphology of Fe-containing intermetallics. •Cr- and Mn-dispersoids formed in the aluminium matrix during solution treatment. •Dispersion hardening was detected after solution treatment for Cr-containing alloy. •The dispersion hardening effect was maintained after ageing treatment.« less

Effect of Nano-Si3N4 Additives and Plasma Treatment on the Dry Sliding Wear Behavior of Plasma Sprayed Al2O3-8YSZ Ceramic Coatings

NASA Astrophysics Data System (ADS)

Gou, Junfeng; Zhang, Jian; Zhang, Qiwen; Wang, You; Wang, Chaohui

2017-04-01

In this paper, the effect of nano-Si3N4 additives and plasma treatment on the wear behavior of Al2O3-8YSZ ceramic coatings was studied. Nano-Al2O3, nano-8YSZ (8 wt.% Y2O3-stabilized ZrO2) and nano-Si3N4 powders were used as raw materials to fabricate four types of sprayable feedstocks. Plasma treatment was used to improve the properties of the feedstocks. The surface morphologies of the ceramic coatings were observed. The mechanical properties of the ceramic coatings were measured. The dry sliding wear behavior of the Al2O3-8YSZ coatings with and without Si3N4 additives was studied. Nano-Si3N4 additives and plasma treatment can improve the morphologies of the coatings by prohibiting the initiation of micro-cracks and reducing the unmelted particles. The hardness and bonding strength of AZSP (Al2O3-18 wt.% 8YSZ-10 wt.% Si3N4-plasma treatment) coating increased by 79.2 and 44% compared to those of AZ (Al2O3-20 wt.% 8YSZ) coating. The porosity of AZSP coating decreased by 85.4% compared to that of AZ coating. The wear test results showed that the addition of nano-Si3N4 and plasma treatment could improve the wear resistance of Al2O3-8YSZ coatings.

High temperature compounds for turbine vanes. [of SiC, Si3N4, and Si composites

NASA Technical Reports Server (NTRS)

Rhodes, W. H.; Cannon, R. M., Jr.

1974-01-01

Fabrication and microstructure control studies were conducted on SiC, Si3N and composites based on Si3N. Charpy mode impact testing to 2400 F established that Si3N4/Mo composites have excellent potential. Attempts to fabricate composites of Si3N4 with superalloys, both by hot pressing and infiltration were largely unsuccessful in comparison to using Mo, Re, and Ta which are less reactive. Modest improvements in impact strength were realized for monolithic Si3N4; however, SiC strengths increased by a factor of six and now equal values achieved for Si3N4. Correlations of impact strength with material properties are discussed. Reduced MgO densification aid additions to Si3N4 were found to decrease densification kinetics, increase final porosity, decrease room temperature bend strength, increase high temperature bend strength, and decrease bend stress rupture properties. The decrease in bend strength at high temperature for fine grain size SiC suggested that a slightly larger grain size material with a nearly constant strength-temperature relation may prove desirable in the creep and stress rupture mode.

An Isotope Study of Hydrogenation of poly-Si/SiOx Passivated Contacts for Si Solar Cells: Preprint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schnabel, Manuel; Nemeth, William; van de Loo, Bas, W.H.

2017-06-26

For many years, the record Si solar cell efficiency stood at 25.0%. Only recently have several companies and institutes managed to produce more efficient cells, using passivated contacts of made doped poly-Si or a-Si:H and a passivating intrinsic interlayer in all cases. Common to these designs is the need to passivate the layer stack with hydrogen. In this contribution, we perform a systematic study of passivated contact passivation by hydrogen, using poly-Si/SiOx passivated contacts on n-Cz-Si, and ALD Al2O3 followed by a forming gas anneal (FGA) as the hydrogen source. We study p-type and n-type passivated contacts with implied Vocmore » exceeding 690 and 720 mV, respectively, and perform either the ALD step or the FGA with deuterium instead of hydrogen in order to separate the two processes via SIMS. By examining the deuterium concentration at the SiOx in both types of samples, we demonstrate that the FGA supplies negligible hydrogen species to the SiOx, regardless of whether the FGA is hydrogenated or deuterated. Instead, it supplies the thermal energy needed for hydrogen species in the Al2O3 to diffuse there. Furthermore, the concentration of hydrogen species at the SiOx can saturate while implied Voc continues to increase, showing that the energy from the FGA is also required for hydrogen species already at the SiOx to find recombination-active defects to passivate.« less

The Abundance of SiC2 in Carbon Star Envelopes⋆: Evidence that SiC2 is a gas-phase precursor of SiC dust

PubMed Central

Massalkhi, Sarah; Agúndez, M.; Cernicharo, J.; Velilla Prieto, L.; Goicoechea, J. R.; Quintana-Lacaci, G.; Fonfría, J. P.; Alcolea, J.; Bujarrabal, V.

2017-01-01

Context Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si–C bond detected in C-rich AGB stars are SiC2, SiC, and Si2C. To date, the ring molecule SiC2 has been observed in a handful of evolved stars, while SiC and Si2C have only been detected in the C-star envelope IRC +10216. Aims We aim to study how widespread and abundant SiC2, SiC, and Si2C are in envelopes around C-rich AGB stars and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars. Methods We carried out sensitive observations with the IRAM 30m telescope of a sample of 25 C-rich AGB stars to search for emission lines of SiC2, SiC, and Si2C in the λ 2 mm band. We performed non-LTE excitation and radiative transfer calculations based on the LVG method to model the observed lines of SiC2 and to derive SiC2 fractional abundances in the observed envelopes. Results We detect SiC2 in most of the sources, SiC in about half of them, and do not detect Si2C in any source, at the exception of IRC +10216. Most of these detections are reported for the first time in this work. We find a positive correlation between the SiC and SiC2 line emission, which suggests that both species are chemically linked, the SiC radical probably being the photodissociation product of SiC2 in the external layer of the envelope. We find a clear trend in which the denser the envelope, the less abundant SiC2 is. The observed trend is interpreted as an evidence of efficient incorporation of SiC2 onto dust grains, a process which is favored at high densities owing to the higher rate at which collisions between particles take place. Conclusions The observed behavior of a decline in the SiC2 abundance with increasing density strongly suggests that SiC2 is an important

Hydrogen passivation of poly-Si/SiO x contacts for Si solar cells using Al 2O 3 studied with deuterium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schnabel, Manuel; van de Loo, Bas W. H.; Nemeth, William

Here, the interplay between hydrogenation and passivation of poly-Si/SiO x contacts to n-type Si wafers is studied using atomic layer deposited Al 2O 3 and anneals in forming gas and nitrogen. The poly-Si/SiO x stacks are prepared by thermal oxidation followed by thermal crystallization of a-Si:H films deposited by plasma-enhanced chemical vapor deposition. Implied open-circuit voltages as high as 710 mV are achieved for p-type poly-Si/SiO x contacts to n-type Si after hydrogenation. Correlating minority carrier lifetime data and secondary ion mass spectrometry profiles reveals that the main benefit of Al 2O 3 is derived from its role as amore » hydrogen source for chemically passivating defects at SiO x; Al 2O 3 layers are found to hydrogenate poly-Si/SiO x much better than a forming gas anneal. By labelling Al 2O 3 and the subsequent anneal with different hydrogen isotopes, it is found that Al 2O 3 exchanges most of its hydrogen with the ambient upon annealing at 400 °C for 1 h even though there is no significant net change in its total hydrogen content.« less

Hydrogen passivation of poly-Si/SiO x contacts for Si solar cells using Al 2O 3 studied with deuterium

DOE PAGES

Schnabel, Manuel; van de Loo, Bas W. H.; Nemeth, William; ...

2018-05-14

Here, the interplay between hydrogenation and passivation of poly-Si/SiO x contacts to n-type Si wafers is studied using atomic layer deposited Al 2O 3 and anneals in forming gas and nitrogen. The poly-Si/SiO x stacks are prepared by thermal oxidation followed by thermal crystallization of a-Si:H films deposited by plasma-enhanced chemical vapor deposition. Implied open-circuit voltages as high as 710 mV are achieved for p-type poly-Si/SiO x contacts to n-type Si after hydrogenation. Correlating minority carrier lifetime data and secondary ion mass spectrometry profiles reveals that the main benefit of Al 2O 3 is derived from its role as amore » hydrogen source for chemically passivating defects at SiO x; Al 2O 3 layers are found to hydrogenate poly-Si/SiO x much better than a forming gas anneal. By labelling Al 2O 3 and the subsequent anneal with different hydrogen isotopes, it is found that Al 2O 3 exchanges most of its hydrogen with the ambient upon annealing at 400 °C for 1 h even though there is no significant net change in its total hydrogen content.« less

The role of groundwater discharge fluxes on Si:P ratios in a major tributary to Lake Erie.

PubMed

Maavara, Taylor; Slowinski, Stephanie; Rezanezhad, Fereidoun; Van Meter, Kimberly; Van Cappellen, Philippe

2018-05-01

Groundwater discharge can be a major source of nutrients to river systems. Although quantification of groundwater nitrate loading to streams is common, the dependence of surface water silicon (Si) and phosphorus (P) concentrations on groundwater sources has rarely been determined. Additionally, the ability of groundwater discharge to drive surface water Si:P ratios has not been contextualized relative to riverine inputs or in-stream transformations. In this study, we quantify the seasonal dynamics of Si and P cycles in the Grand River (GR) watershed, the largest Canadian watershed draining into Lake Erie, to test our hypothesis that regions of Si-rich groundwater discharge increase surface water Si:P ratios. Historically, both the GR and Lake Erie have been considered stoichiometrically P-limited, where the molar Si:P ratio is greater than the ~16:1 phytoplankton uptake ratio. However, recent trends suggest that eastern Lake Erie may be approaching Si-limitation. We sampled groundwater and surface water for dissolved and reactive particulate Si as well as total dissolved P for 12months within and downstream of a 50-km reach of high groundwater discharge. Our results indicate that groundwater Si:P ratios are lower than the corresponding surface water and that groundwater is a significant source of bioavailable P to surface water. Despite these observations, the watershed remains P-limited for the majority of the year, with localized periods of Si-limitation. We further find that groundwater Si:P ratios are a relatively minor driver of surface water Si:P, but that the magnitude of Si and P loads from groundwater represent a large proportion of the overall fluxes to Lake Erie. Copyright © 2017 Elsevier B.V. All rights reserved.

Development and Characterization of SiC)/ MoSi2-Si3N4(p) Hybrid Composites

NASA Technical Reports Server (NTRS)

Hebsur, Mohan G.

1998-01-01

Intermetallic compound MoSi2 has long been known as a high temperature material that has excellent oxidation resistance and electrical/thermal conductivity. Also its low cost, high melting point (2023 C), relatively low density (6.2 g/cu cm versus 9 g/cu cm for current engine materials), and ease of machining, make it an attractive structural material. However, the use of MoSi2 has been hindered due to its poor toughness at low temperatures, poor creep resistance at high temperatures, and accelerated oxidation (also known as 'pest' oxidation) at temperatures between approximately 450 and 550 C. Continuous fiber reinforcing is very effective means of improving both toughness and strength. Unfortunately, MoSi2 has a relatively high coefficient of thermal expansion (CTE) compared to potential reinforcing fibers such as SiC. The large CTE mismatch between the fiber and the matrix resulted in severe matrix cracking during thermal cycling. Addition of about 30 to 50 vol % of Si3N4 particulate to MoSi2 improved resistance to low temperature accelerated oxidation by forming a Si2ON2 protective scale and thereby eliminating catastrophic 'pest failure'. The Si3N4 addition also improved the high temperature creep strength by nearly five orders of magnitude, doubled the room temperature toughness and significantly lowered the CTE of the MoSi2 and eliminated matrix cracking in SCS-6 reinforced composites even after thermal cycling. The SCS-6 fiber reinforcement improved the room temperature fracture toughness by seven times and impact resistance by five times. The composite exhibited excellent strength and toughness improvement up to 1400 C. More recently, tape casting was adopted as the preferred processing of MoSi2-base composites for improved fiber spacing, ability to use small diameter fibers, and for lower cost. Good strength and toughness values were also obtained with fine diameter Hi-Nicalon tow fibers. This hybrid composite remains competitive with ceramic matrix

MoSi2-Base Composites

NASA Technical Reports Server (NTRS)

Hebsur, Mohan G.

2003-01-01

Addition of 30 to 50 vol% of Si3N4 particulate to MoSi2 eliminated its low temperature catastrophic failure, improved room temperature fracture toughness and the creep resistance. The hybrid composite SCS-6/MoSi2-Si3N4 did not show any matrix cracking and exhibited excellent mechanical and environmental properties. Hi-Nicalon continuous fiber reinforced MoSi2-Si3N4 also showed good strength and toughness. A new MoSi2-base composite containing in-situ whisker-type (Beta)Si3N4 grains in a MoSi2 matrix is also described.

Escaping the Tyranny of Carbothermal Reduction: Fumed Silica from Sustainable, Green Sources without First Having to Make SiCl4.

PubMed

Yi, Eongyu; Hyde, Clare E; Sun, Kai; Laine, Richard M

2016-02-12

Fumed silica is produced in 1000 tons per year quantities by combusting SiCl4 in H2 /O2 flames. Given that both SiCl4 and combustion byproduct HCl are corrosive, toxic and polluting, this route to fumed silica requires extensive safeguards that may be obviated if an alternate route were found. Silica, including rice hull ash (RHA) can be directly depolymerized using hindered diols to generate distillable spirocyclic alkoxysilanes or Si(OEt)4 . We report here the use of liquid-feed flame spray pyrolysis (LF-FSP) to combust the aforementioned precursors to produce fumed silica very similar to SiCl4 -derived products. The resulting powders are amorphous, necked, <50 nm average particle sizes, with specific surface areas (SSAs) of 140-230 m(2)  g(-1) . The LF-FSP approach does not require the containment constraints of the SiCl4 process and given that the RHA silica source is produced in million ton per year quantities worldwide, the reported approach represents a sustainable, green and potentially lower-cost alternative. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

CVD of SiC and AlN using cyclic organometallic precursors

NASA Technical Reports Server (NTRS)

Interrante, L. V.; Larkin, D. J.; Amato, C.

1992-01-01

The use of cyclic organometallic molecules as single-source MOCVD precursors is illustrated by means of examples taken from our recent work on AlN and SiC deposition, with particular focus on SiC. Molecules containing (AlN)3 and (SiC)2 rings as the 'core structure' were employed as the source materials for these studies. The organoaluminum amide, (Me2AlNH2)3, was used as the AlN source and has been studied in a molecular beam sampling apparatus in order to determine the gas phase species present in a hot-wall CVD reactor environment. In the case of SiC CVD, a series of disilacyclobutanes (Si(XX')CH2)2 (with X and X' = H, CH3, and CH2SiH2CH3), were examined in a cold-wall, hot-stage CVD reactor in order to compare their relative reactivities and prospective utility as single-source CVD precursors. The parent compound, disilacyclobutane, (SiH2CH2)2, was found to exhibit the lowest deposition temperature (ca. 670 C) and to yield the highest purity SiC films. This precursor gave a highly textured, polycrystalline film on the Si(100) substrates.

Novel microstructural growth in the surface of Inconel 625 by the addition of SiC under electron beam melting

NASA Astrophysics Data System (ADS)

Ahmad, M.; Ali, G.; Ahmed, Ejaz; Haq, M. A.; Akhter, J. I.

2011-06-01

Electron beam melting is being used to modify the microstructure of the surfaces of materials due to its ability to cause localized melting and supercooling of the melt. This article presents an experimental study on the surface modification of Ni-based superalloy (Inconel 625) reinforced with SiC ceramic particles under electron beam melting. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction techniques have been applied to characterize the resulted microstructure. The results revealed growth of novel structures like wire, rod, tubular, pyramid, bamboo and tweezers type morphologies in the modified surface. In addition to that fibrous like structure was also observed. Formation of thin carbon sheet has been found at the regions of decomposed SiC. Electron beam modified surface of Inconel 625 alloy has been hardened twice as compared to the as-received samples. Surface hardening effect may be attributed to both the formation of the novel structures as well as the introduction of Si and C atom in the lattice of Inconel 625 alloy.

Si /SiGe n-type resonant tunneling diodes fabricated using in situ hydrogen cleaning

NASA Astrophysics Data System (ADS)

Suet, Z.; Paul, D. J.; Zhang, J.; Turner, S. G.

2007-05-01

In situ hydrogen cleaning to reduce the surface segregation of n-type dopants in SiGe epitaxy has been used to fabricate Si /SiGe resonant tunneling diodes in a joint gas source chemical vapor deposition and molecular beam epitaxial system. Diodes fabricated without the in situ clean demonstrate linear current-voltage characteristics, while a 15min hydrogen clean produces negative differential resistance with peak-to-valley current ratios up to 2.2 and peak current densities of 5.0A/cm2 at 30K. Analysis of the valley current and the band structure of the devices suggest methods for increasing the operating temperature of Si /SiGe resonant tunneling diodes as required for applications.

Effect of Mn and AlTiB Addition and Heattreatment on the Microstructures and Mechanical Properties of Al-Si-Fe-Cu-Zr Alloy.

PubMed

Yoo, Hyo-Sang; Kim, Yong-Ho; Lee, Seong-Hee; Son, Hyeon-Taek

2018-09-01

The microstructure and mechanical properties of as-extruded Al-0.1 wt%Si-0.2 wt%Fe- 0.4 wt%Cu-0.04 wt%Zr-xMn-xAlTiB (x = 1.0 wt%) alloys under various annealing processes were investigated and compared. After the as-cast billets were kept at 400 °C for 1 hr, hot extrusion was carried out with a reduction ratio of 38:1. In the case of the as-extruded Al-Si-Fe-Cu-Zr alloy at annealed at 620 °C, large equiaxed grain was observed. When the Mn content is 1.0 wt%, the phase exhibits a skeleton morphology, the phase formation in which Mn participated. Also, the volume fraction of the intermetallic compounds increased with Mn and AlTiB addition. For the Al-0.1Si-0.2Fe-0.4Cu-0.04Zr alloy with Mn and AlTiB addition from 1.0 wt%, the ultimate tensile strength increased from 100.47 to 119.41 to 110.49 MPa. The tensile strength of the as-extruded alloys improved with the addition of Mn and AlTiB due to the formation of Mn and AlTiB-containing intermetallic compounds.

From Si wafers to cheap and efficient Si electrodes for Li-ion batteries

NASA Astrophysics Data System (ADS)

Gauthier, Magali; Reyter, David; Mazouzi, Driss; Moreau, Philippe; Guyomard, Dominique; Lestriez, Bernard; Roué, Lionel

2014-06-01

High-energy ball milling is used to recycle Si wafers to produce Si powders for negative electrodes of Li-ion batteries. The resulting Si powder consists in micrometric Si agglomerates made of cold-welded submicrometric nanocrystalline Si particles. Silicon-based composite electrodes prepared with ball-milled Si wafer can achieve more than 900 cycles with a capacity of 1200 mAh g-1 of Si (880 mAh g-1 of electrode) and a coulombic efficiency higher than 99%. This excellent electrochemical performance lies in the use of nanostructured Si produced by ball milling, the electrode formulation in a pH 3 buffer solution with CMC as binder and the use of FEC/VC additives in the electrolyte. This work opens the way to an economically attractive recycling of Si wastes.

SEMICONDUCTOR TECHNOLOGY: SBH adjustment characteristic of the dopant segregation process for NiSi/n-Si SJDs

NASA Astrophysics Data System (ADS)

Haiping, Shang; Qiuxia, Xu

2010-05-01

By means of analyzing the I-V characteristic curve of NiSi/n-Si Schottky junction diodes (NiSi/n-Si SJDs), abstracting the effective Schottky barrier height (varphiB, eff) and the ideal factor of NiSi/n-Si SJDs and measuring the sheet resistance of NiSi films (RNiSi), we study the effects of different dopant segregation process parameters, including impurity implantation dose, segregation annealing temperature and segregation annealing time, on the varphiB, eff of NiSi/n-Si SJDs and the resistance characteristic of NiSi films. In addition, the changing rules of varphiB, eff and RNiSi are discussed.

Na@SiO2-Mediated Addition of Organohalides to Carbonyl Compounds for the Formation of Alcohols and Epoxides

NASA Astrophysics Data System (ADS)

Kapoor, Mohit; Hwu, Jih Ru

2016-11-01

Alcohols and epoxides were generated by the addition of organohalides to carbonyl compounds in the presence of sodium metal impregnated with silica gel (Na@SiO2) in THF at 25 °C through a radical pathway. Under the same conditions, Schiff bases were also successfully converted to the corresponding amines. Furthermore, the reaction of aldehydes with α-haloesters or 4-(chloromethyl)-coumarin with the aid of Na@SiO2 generated trans epoxides. An unprecedented mechanism is proposed for their formation. The advantages associated with these new reactions include: (1) products are obtained in good-to-excellent yields, (2) reactions are completed at room temperatures in a short period of time (<2.0 h), (3) it is unnecessary to perform the reactions under anhydrous conditions, and (4) the entire process requires only simple manipulations.

Influence wt.% of SiC and borax on the mechanical properties of AlSi-Mg-TiB-SiC composite by the method of semi solid stir casting

NASA Astrophysics Data System (ADS)

Bhiftime, E. I.; Guterres, Natalino F. D. S.; Haryono, M. B.; Sulardjaka, Nugroho, Sri

2017-04-01

SiC particle reinforced metal matrix composites (MMCs) with solid semi stir casting method is becoming popular in recent application (automotive, aerospace). Stirring the semi solid condition is proven to enhance the bond between matrix and reinforcement. The purpose of this study is to investigate the effect of the SiC wt.% and the addition of borax on mechanical properties of composite AlSi-Mg-TiB-SiC and AlSi-Mg-TiB-SiC/Borax. Specimens was tested focusing on the density, porosity, tensile test, impact test microstructure and SEM. AlSi is used as a matrix reinforced by SiC with percentage variations (10, 15, 20 wt.%). Giving wt.% Borax which is the ratio of 1: 4 between wt.% SiC. The addition of 1.5% of TiB gives grain refinement. The use of semi-solid stir casting method is able to increase the absorption of SiC particles into a matrix AlSi evenly. The improved composite presented here can be used as a guideline to make a new composite.

Characterization of SiGe thin films using a laboratory X-ray instrument.

PubMed

Ulyanenkova, Tatjana; Myronov, Maksym; Benediktovitch, Andrei; Mikhalychev, Alexander; Halpin, John; Ulyanenkov, Alex

2013-08-01

The technique of reciprocal space mapping using X-rays is a recognized tool for the nondestructive characterization of epitaxial films. X-ray scattering from epitaxial Si 0.4 Ge 0.6 films on Si(100) substrates using a laboratory X-ray source was investigated. It is shown that a laboratory source with a rotating anode makes it possible to investigate the material parameters of the super-thin 2-6 nm layers. For another set of partially relaxed layers, 50-200 nm thick, it is shown that from a high-resolution reciprocal space map, conditioned from diffuse scattering on dislocations, it is possible to determine quantitatively from the shape of a diffraction peak (possessing no thickness fringes) additional parameters such as misfit dislocation density and layer thickness as well as concentration and relaxation.

Naturally occurring 32Si and low-background silicon dark matter detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orrell, John L.; Arnquist, Isaac J.; Bliss, Mary

Here, the naturally occurring radioisotope 32Si represents a potentially limiting background in future dark matter direct-detection experiments. We investigate sources of 32Si and the vectors by which it comes to reside in silicon crystals used for fabrication of radiation detectors. We infer that the 32Si concentration in commercial single-crystal silicon is likely variable, dependent upon the specific geologic and hydrologic history of the source (or sources) of silicon “ore” and the details of the silicon-refinement process. The silicon production industry is large, highly segmented by refining step, and multifaceted in terms of final product type, from which we conclude thatmore » production of 32Si-mitigated crystals requires both targeted silicon material selection and a dedicated refinement-through-crystal-production process. We review options for source material selection, including quartz from an underground source and silicon isotopically reduced in 32Si. To quantitatively evaluate the 32Si content in silicon metal and precursor materials, we propose analytic methods employing chemical processing and radiometric measurements. Ultimately, it appears feasible to produce silicon detectors with low levels of 32Si, though significant assay method development is required to validate this claim and thereby enable a quality assurance program during an actual controlled silicon-detector production cycle.« less

Naturally occurring 32Si and low-background silicon dark matter detectors

DOE PAGES

Orrell, John L.; Arnquist, Isaac J.; Bliss, Mary; ...

2018-02-10

Here, the naturally occurring radioisotope 32Si represents a potentially limiting background in future dark matter direct-detection experiments. We investigate sources of 32Si and the vectors by which it comes to reside in silicon crystals used for fabrication of radiation detectors. We infer that the 32Si concentration in commercial single-crystal silicon is likely variable, dependent upon the specific geologic and hydrologic history of the source (or sources) of silicon “ore” and the details of the silicon-refinement process. The silicon production industry is large, highly segmented by refining step, and multifaceted in terms of final product type, from which we conclude thatmore » production of 32Si-mitigated crystals requires both targeted silicon material selection and a dedicated refinement-through-crystal-production process. We review options for source material selection, including quartz from an underground source and silicon isotopically reduced in 32Si. To quantitatively evaluate the 32Si content in silicon metal and precursor materials, we propose analytic methods employing chemical processing and radiometric measurements. Ultimately, it appears feasible to produce silicon detectors with low levels of 32Si, though significant assay method development is required to validate this claim and thereby enable a quality assurance program during an actual controlled silicon-detector production cycle.« less

Naturally occurring 32Si and low-background silicon dark matter detectors

NASA Astrophysics Data System (ADS)

Orrell, John L.; Arnquist, Isaac J.; Bliss, Mary; Bunker, Raymond; Finch, Zachary S.

2018-05-01

The naturally occurring radioisotope 32Si represents a potentially limiting background in future dark matter direct-detection experiments. We investigate sources of 32Si and the vectors by which it comes to reside in silicon crystals used for fabrication of radiation detectors. We infer that the 32Si concentration in commercial single-crystal silicon is likely variable, dependent upon the specific geologic and hydrologic history of the source (or sources) of silicon "ore" and the details of the silicon-refinement process. The silicon production industry is large, highly segmented by refining step, and multifaceted in terms of final product type, from which we conclude that production of 32Si-mitigated crystals requires both targeted silicon material selection and a dedicated refinement-through-crystal-production process. We review options for source material selection, including quartz from an underground source and silicon isotopically reduced in 32Si. To quantitatively evaluate the 32Si content in silicon metal and precursor materials, we propose analytic methods employing chemical processing and radiometric measurements. Ultimately, it appears feasible to produce silicon detectors with low levels of 32Si, though significant assay method development is required to validate this claim and thereby enable a quality assurance program during an actual controlled silicon-detector production cycle.

Naturally occurring 32 Si and low-background silicon dark matter detectors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Orrell, John L.; Arnquist, Isaac J.; Bliss, Mary

The naturally occurring radioisotope Si-32 represents a potentially limiting background in future dark matter direct-detection experiments. We investigate sources of Si-32 and the vectors by which it comes to reside in silicon crystals used for fabrication of radiation detectors. We infer that the Si-32 concentration in commercial single-crystal silicon is likely variable, dependent upon the specific geologic and hydrologic history of the source (or sources) of silicon “ore” and the details of the silicon-refinement process. The silicon production industry is large, highly segmented by refining step, and multifaceted in terms of final product type, from which we conclude that productionmore » of Si-32-mitigated crystals requires both targeted silicon material selection and a dedicated refinement-through-crystal-production process. We review options for source material selection, including quartz from an underground source and silicon isotopically reduced in Si-32. To quantitatively evaluate the Si-32 content in silicon metal and precursor materials, we propose analytic methods employing chemical processing and radiometric measurements. Ultimately, it appears feasible to produce silicon-based detectors with low levels of Si-32, though significant assay method development is required to validate this claim and thereby enable a quality assurance program during an actual controlled silicon-detector production cycle.« less

Low Temperature Deposition of PECVD Polycrystalline Silicon Thin Films using SiF4 / SiH4 mixture

NASA Astrophysics Data System (ADS)

Syed, Moniruzzaman; Inokuma, Takao; Kurata, Yoshihiro; Hasegawa, Seiichi

2016-03-01

Polycrystalline silicon films with a strong (110) texture were prepared at 400°C by a plasma-enhanced chemical vapor deposition using different SiF4 flow rates ([SiF4] = 0-0.5 sccm) under a fixed SiH4 flow rate ([SiH4] = 1 or 0.15 sccm). The effects of the addition of SiF4 to SiH4 on the structural properties of the films were studied by Raman scattering, X-ray diffraction (XRD), Atomic force microscopy and stress measurements. For [SiH4] = 1 sccm, the crystallinity and the (110) XRD grain size monotonically increased with increasing [SiF4] and their respective maxima reach 90% and 900 Å. However, for [SiH4] = 0.15 sccm, both the crystallinity and the grain size decreased with [SiF4]. Mechanisms causing the change in crystallinity are discussed, and it was suggested that an improvement in the crystallinity, due to the addition of SiF4, is likely to be caused by the effect of a change in the surface morphology of the substrates along with the effect of in situ chemical cleaning.

Kinetic manipulation of silicide phase formation in Si nanowire templates.

PubMed

Chen, Yu; Lin, Yung-Chen; Zhong, Xing; Cheng, Hung-Chieh; Duan, Xiangfeng; Huang, Yu

2013-08-14

The phase formation sequence of silicides in two-dimensional (2-D) structures has been well-investigated due to their significance in microelectronics. Applying high-quality silicides as contacts in nanoscale silicon (Si) devices has caught considerable attention recently for their potential in improving and introducing new functions in nanodevices. However, nucleation and diffusion mechanisms are found to be very different in one-dimensional (1-D) nanostructures, and thus the phase manipulation of silicides is yet to be achieved there. In this work, we report kinetic phase modulations to selectively enhance or hinder the growth rates of targeted nickel (Ni) silicides in a Si nanowire (NW) and demonstrate that Ni31Si12, δ-Ni2Si, θ-Ni2Si, NiSi, and NiSi2 can emerge as the first contacting phase at the silicide/Si interface through these modulations. First, the growth rates of silicides are selectively tuned through template structure modifications. It is demonstrated that the growth rate of diffusion limited phases can be enhanced in a porous Si NW due to a short diffusion path, which suppresses the formation of interface limited NiSi2. In addition, we show that a confining thick shell can be applied around the Si NW to hinder the growth of the silicides with large volume expansion during silicidation, including Ni31Si12, δ-Ni2Si, and θ-Ni2Si. Second, a platinum (Pt) interlayer between the Ni source and the Si NW is shown to effectively suppress the formation of the phases with low Pt solubility, including the dominating NiSi2. Lastly, we show that with the combined applications of the above-mentioned approaches, the lowest resistive NiSi phase can form as the first phase in a solid NW with a Pt interlayer to suppress NiSi2 and a thick shell to hinder Ni31Si12, δ-Ni2Si, and θ-Ni2Si simultaneously. The resistivity and maximum current density of NiSi agree reasonably to reported values.

Effects of Ti addition and heat treatments on mechanical and electrical properties of Cu-Ni-Si alloys

NASA Astrophysics Data System (ADS)

Kim, Hyung Giun; Lee, Taeg Woo; Kim, Sang Min; Han, Seung Zeon; Euh, Kwangjun; Kim, Won Yong; Lim, Sung Hwan

2013-01-01

The mechanical and electrical properties of Cu-5.98Ni-1.43Si and Cu-5.98Ni-1.29Si-0.24Ti alloys under heat treatment at 400 and 500 °C after hot- and cold-rolling were investigated, and a microstructural analysis using transmission electron microscopy was performed. Cu-5.98Ni-1.29Si-0.24Ti alloy displayed the combined Vickers hardness/electrical conductivity value of 315.9 Hv/57.1%IACS. This was attributed to a decrease of the solution solubility of Ni and Si in the Cu matrix by the formation of smaller and denser δ-Ni2Si precipitates. Meanwhile, the alloyed Ti was detected in the coarse Ni-Si-Ti phase particles, along with other large Ni-Si phase particles, in Cu-5.98Ni-1.29Si-0.24Ti.

Adsorption and dynamics of Si atoms at the monolayer Pb/Si(111) surface

NASA Astrophysics Data System (ADS)

Kumar, Rakesh; Fang, Chuang-Kai; Lee, Chih-Hao; Hwang, Ing-Shouh

2017-06-01

In this work, we studied the adsorption behavior of deposited Si atoms along with their diffusion and other dynamic processes on a Pb monolayer-covered Si(111) surface from 125 to 230 K using a variable-temperature scanning tunneling microscope. The Pb-covered Si(111) surface forms a low-symmetry rowlike (√{7 }×√{3 } ) structure in this temperature range and the Si atoms bind favorably to two specific on-top sites (T1 A and T1 B) on the trimer row after deposition at the sample temperature of ˜125 K . The Si atoms were immobile at low temperatures and started to switch between the two neighboring T1 A and T1 B sites within the same trimer when the temperature was raised to ˜150 K . When the temperature was raised above ˜160 K , the adsorbed Si atoms could hop to other trimers along the same trimer row. Below ˜170 K , short hops to adjacent trimers dominated, but long hops dominated at temperatures above ˜170 K . The activation energy and prefactor for the Si atoms diffusion were derived through analysis of continuous-time imaging at temperatures from 160 to 174 K. In addition, irreversible aggregation of single Si atoms into Si clusters started to occur at the phase boundaries or defective sites at temperatures above ˜170 K . At temperature above ˜180 K , nearly all Si atoms aggregated into clusters, which may have important implications for the atomic mechanism of epitaxial growth of Si on the Pb-covered Si(111) surface. In addition, our study provides strong evidence for breaking in the mirror symmetry in the (√{7 }×√{3 } )-Pb structure, which has implications for the atomic model of this controversial structure.

Transport properties of Sb doped Si nanowires

NASA Astrophysics Data System (ADS)

Nukala, Prathyusha; Sapkota, Gopal; Gali, Pradeep; Usha, Philipose

2011-10-01

n-type Si nanowires were synthesized at ambient pressure using SiCl4 as Si source and Sb source as the dopant. Sb doping of 3-4 wt % was achieved through a post growth diffusion technique. The nanowires were found to have an amorphous oxide shell that developed post-growth; the thickness of the shell is estimated to be about 3-4 nm. The composition of the amorphous shell covering the crystalline Si core was determined by Raman spectroscopy, with evidence that the shell was an amorphous oxide layer. Optical characterization of the as-grown nanowires showed green emission, attributed to the presence of the oxide shell covering the Si nanowire core. Etching of the oxide shell was found to decrease the intensity of this green emission. A single undoped Si nanowire contacted in an FET type configuration was found to be p-type with channel mobility of 20 cm^2V-1S-1. Sb doped Si nanowires exhibited n-type behavior, compensating for the holes in the undoped nanowire. The doped nanowires had carrier mobility and concentration of 160 cm^2V-1S-1 and 9.6 x 10^18cm-3 respectively.

SiS in Circumstellar Shells

NASA Astrophysics Data System (ADS)

Sahai, R.; Wootten, A.; Clegg, R. E. S.

1985-07-01

The author has observed the spectrum of SiS toward the Mira variable IRC+10216, and made a detailed model incorporating a radial SiS abundance gradient due to photodissociation by interstellar UV (Sahai, Wootten, and Clegg 1984). The sensitive search for SiS J = 7-6 and J = 6-5 lines in other carbon-rich, oxygen-rich, and S-type envelopes has revealed three new sources, CIT 6, CRL 2688 and IRC+20370, all of which are carbon-rich.

Characterization of SiGe thin films using a laboratory X-ray instrument

PubMed Central

Ulyanenkova, Tatjana; Myronov, Maksym; Benediktovitch, Andrei; Mikhalychev, Alexander; Halpin, John; Ulyanenkov, Alex

2013-01-01

The technique of reciprocal space mapping using X-rays is a recognized tool for the nondestructive characterization of epitaxial films. X-ray scattering from epitaxial Si0.4Ge0.6 films on Si(100) substrates using a laboratory X-ray source was investigated. It is shown that a laboratory source with a rotating anode makes it possible to investigate the material parameters of the super-thin 2–6 nm layers. For another set of partially relaxed layers, 50–200 nm thick, it is shown that from a high-resolution reciprocal space map, conditioned from diffuse scattering on dislocations, it is possible to determine quantitatively from the shape of a diffraction peak (possessing no thickness fringes) additional parameters such as misfit dislocation density and layer thickness as well as concentration and relaxation. PMID:24046495

Low Activation Joining of SiC/SiC Composites for Fusion Applications: Modeling Thermal and Irradiation-induced Swelling Effects on Integrity of Ti3SiC2/SiC Joint

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nguyen, Ba Nghiep; Henager, Charles H.; Kurtz, Richard J.

This work developed a continuum damage mechanics model that incorporates thermal expansion combined with irradiation-induced swelling effects to study the origin of cracking observed in recent irradiation experiments. Micromechanical modeling using an Eshelby-Mori-Tanaka approach was used to compute the thermoelastic properties of the Ti3SiC2/SiC joint needed for the model. In addition, a microstructural dual-phase Ti3SiC2/SiC model was developed to determine irradiation-induced swelling of the composite joint at a given temperature resulting from differential swelling of SiC and the Ti3SiC2 MAX phase. Three cases for the miniature torsion hourglass (THG) specimens containing a Ti3SiC2/SiC joint were analyzed corresponding to three irradiationmore » temperatures: 800oC, 500oC, and 400oC.« less

X-ray absorption spectroscopy study on SiC-side interface structure of SiO2–SiC formed by thermal oxidation in dry oxygen

NASA Astrophysics Data System (ADS)

Isomura, Noritake; Kosaka, Satoru; Kataoka, Keita; Watanabe, Yukihiko; Kimoto, Yasuji

2018-06-01

Extended X-ray absorption fine structure (EXAFS) spectroscopy is demonstrated to measure the fine atomic structure of SiO2–SiC interfaces. The SiC-side of the interface can be measured by fabricating thin SiO2 films and using SiC-selective EXAFS measurements. Fourier transforms of the oscillations of the EXAFS spectra correspond to radial-structure functions and reveal a new peak of the first nearest neighbor of Si for m-face SiC, which does not appear in measurements of the Si-face. This finding suggests that the m-face interface could include a structure with shorter Si–C distances. Numerical calculations provide additional support for this finding.

Metal Additive Manufacturing: A Review of Mechanical Properties

NASA Astrophysics Data System (ADS)

Lewandowski, John J.; Seifi, Mohsen

2016-07-01

This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and directed energy deposition (e.g., LENS, EBF3). Although only a limited number of metallic alloy systems are currently available for additive manufacturing (e.g., Ti-6Al-4V, TiAl, stainless steel, Inconel 625/718, and Al-Si-10Mg), the bulk of the published mechanical properties information has been generated on Ti-6Al-4V. However, summary tables for published mechanical properties and/or key figures are included for each of the alloys listed above, grouped by the additive technique used to generate the data. Published values for mechanical properties obtained from hardness, tension/compression, fracture toughness, fatigue crack growth, and high cycle fatigue are included for as-built, heat-treated, and/or HIP conditions, when available. The effects of test orientation/build direction on properties, when available, are also provided, along with discussion of the potential source(s) (e.g., texture, microstructure changes, defects) of anisotropy in properties. Recommendations for additional work are also provided.

Prediction of 4H-SiC betavoltaic microbattery characteristics based on practical Ni-63 sources.

PubMed

Gui, Gui; Zhang, Kan; Blanchard, James P; Ma, Zhenqiang

2016-01-01

We have investigated the performance of 4H-SiC betavoltaic microbatteries under exposure to the practical Ni-63 sources using the Monte Carlo method and Synopsys® Medici device simulator. A typical planar p-n junction betavoltaic device with the Ni-63 source of 20% purity on top is modeled in the simulation. The p-n junction structure includes a p+ layer, a p- layer, an n+ layer, and an n- layer. In order to obtain an accurate and valid predication, our simulations consider several practical factors, including isotope impurities, self-absorption, and full beta energy spectra. By simulating the effects of both the p-n junction configuration and the isotope source thickness on the battery output performance, we have achieved the optimal design of the device and maximum energy conversion efficiency. Our simulation results show that the energy conversion efficiency increases as the doping concentration and thickness of the p- layer increase, whereas it is independent of the total depth of the p-n junction. Furthermore, the energy conversion efficiency decreases as the thickness of the practical Ni-63 source increases, because of self-absorption in the isotope source. Therefore, we propose that a p-n junction betavoltaic cell with a thicker and heavily doped p- layer under exposure to a practical Ni-63 source with an appreciable thickness could produce the optimal energy conversion efficiency. Copyright © 2015 Elsevier Ltd. All rights reserved.

Tailoring of Boehmite-Derived Aluminosilicate Aerogel Structure and Properties: Influence of Ti Addition

NASA Technical Reports Server (NTRS)

Hurwitz, Frances I.; Guo, Haiquan; Sheets, Erik J.; Miller, Derek R.; Newlin, Katy N.

2010-01-01

Aluminosilicate aerogels offer potential for extremely low thermal conductivities at temperatures greater than 900 C, beyond where silica aerogels reach their upper temperature limits. Aerogels have been synthesized at various Al:Si ratios, including mullite compositions, using Boehmite (AlOOH) as the Al source, and tetraethoxy orthosilicate as the Si precursor. The Boehmite-derived aerogels are found to form by a self-assembly process of AlOOH crystallites, with Si-O groups on the surface of an alumina skeleton. Morphology, surface area and pore size varies with the crystallite size of the starting Boehmite powder, as well as with synthesis parameters. Ternary systems, including Al-Si-Ti aerogels incorporating a soluble Ti precursor, are possible with careful control of pH. The addition of Ti influences sol viscosity, gelation time pore structure and pore size distribution, as well as phase formation on heat treatment.

Thousands of Stellar SiO masers in the Galactic center: The Bulge Asymmetries and Dynamic Evolution (BAaDE) survey

NASA Astrophysics Data System (ADS)

Sjouwerman, Loránt O.; Pihlström, Ylva M.; Rich, R. Michael; Morris, Mark R.; Claussen, Mark J.

2017-01-01

A radio survey of red giant SiO sources in the inner Galaxy and bulge is not hindered by extinction. Accurate stellar velocities (<1 km/s) are obtained with minimal observing time (<1 min) per source. Detecting over 20,000 SiO maser sources yields data comparable to optical surveys with the additional strength of a much more thorough coverage of the highly obscured inner Galaxy. Modeling of such a large sample would reveal dynamical structures and minority populations; the velocity structure can be compared to kinematic structures seen in molecular gas, complex orbit structure in the bar, or stellar streams resulting from recently infallen systems. Our Bulge Asymmetries and Dynamic Evolution (BAaDE) survey yields bright SiO masers suitable for follow-up Galactic orbit and parallax determination using VLBI. Here we outline our early VLA observations at 43 GHz in the northern bulge and Galactic plane (0sources.

Transport properties of Sb-doped Si nanowires

NASA Astrophysics Data System (ADS)

Nukala, Prathyusha; Sapkota, Gopal; Gali, Pradeep; Philipose, U.

2012-08-01

We present a safe and cost-effective approach for synthesis of n-type Sb-doped Si nanowires. The nanowires were synthesized at ambient pressure using SiCl4 as Si source and pure Sb as the dopant source. Structural and compositional characterization using electron microscopy and X-ray spectroscopy show crystalline nanowires with lengths of 30-40 μm and diameters of 40-100 nm. A 3-4 nm thick amorphous oxide shell covers the surface of the nanowire, post-growth. The composition of this shell was confirmed by Raman spectroscopy. Growth of Si nanowires, followed by low temperature annealing in Sb vapor, was shown to be an effective technique for synthesizing Sb-doped Si nanowires. The doping concentration of Sb was found to be dependent on temperature, with Sb re-evaporating from the Si nanowire at higher doping temperatures. Field effect transistors (FETs) were fabricated to investigate the electrical transport properties of these nanowires. The as-grown Si nanowires were found to be p-type with a channel mobility of 40 cm2 V-1 s-1. After doping with Sb, these nanowires exhibited n-type behavior. The channel mobility and carrier concentration of the Sb-doped Si nanowires were estimated to be 288 cm2 V-1 s-1 and 5.3×1018 cm-3 respectively.

Fabrication of Si/ZnS radial nanowire heterojunction arrays for white light emitting devices on Si substrates.

PubMed

Katiyar, Ajit K; Sinha, Arun Kumar; Manna, Santanu; Ray, Samit K

2014-09-10

Well-separated Si/ZnS radial nanowire heterojunction-based light-emitting devices have been fabricated on large-area substrates by depositing n-ZnS film on p-type nanoporous Si nanowire templates. Vertically oriented porous Si nanowires on p-Si substrates have been grown by metal-assisted chemical etching catalyzed using Au nanoparticles. Isolated Si nanowires with needle-shaped arrays have been made by KOH treatment before ZnS deposition. Electrically driven efficient white light emission from radial heterojunction arrays has been achieved under a low forward bias condition. The observed white light emission is attributed to blue and green emission from the defect-related radiative transition of ZnS and Si/ZnS interface, respectively, while the red arises from the porous surface of the Si nanowire core. The observed white light emission from the Si/ZnS nanowire heterojunction could open up the new possibility to integrate Si-based optical sources on a large scale.

Elastic and inelastic properties of SiC/Si biomorphic composites and biomorphic SiC based on oak and eucalyptus

NASA Astrophysics Data System (ADS)

Kardashev, B. K.; Nefagin, A. S.; Smirnov, B. I.; de Arellano-Lopez, A. R.; Martinez-Fernandez, J.; Sepulveda, R.

2006-09-01

This paper reports on the results of a comparative investigation into the elastic and microplastic properties of biomorphic SiC/Si composites and biomorphic SiC prepared by pyrolysis of oak and eucalyptus with subsequent infiltration of molten silicon into a carbon matrix and additional chemical treatment to remove excess silicon. The acoustic studies were performed by the composite oscillator technique using resonant longitudinal vibrations at frequencies of about 100 kHz. It is shown that, in biomorphic SiC (as in biomorphic SiC/Si) at small-amplitude strains ɛ, adsorption and desorption of the environmental (air) molecules determine to a considerable extent the Young’s modulus E and the internal friction (decrement of acoustic vibrations δ) and that the changes in E and δ at these amplitudes are irreversible. The stress-microplastic strain curves are constructed from the acoustic data for the materials under study at temperatures of 100 and 290 K.

NIMROD Modeling of HIT-SI and HIT-SI3

NASA Astrophysics Data System (ADS)

Morgan, Kyle; Jarboe, Tom; Hossack, Aaron

2016-10-01

The HIT-SI and HIT-SI3 devices are spheromaks formed and sustained via a set of Steady Inductive Helicity Injectors (SIHI) that are operated in AC. The experiment explores the formation and sustain of stable spheromaks with a variety of perturbation mode structures. The HIT-SI device consisted of two injectors with primarily n = 1 toroidal symmetry while the HIT-SI3 device has three injectors capable of a mixture of n = 1 and n = 2 perturbations or a primarily n = 3 perturbation, depending on the relative phase of the injectors. Using the NIMROD code to model these devices, we are able to validate with experimental results (previously only done on HIT-SI) and examine the interaction between the injectors and the spheromak. Simulations are performed with both finite and zero- β models to gain an understanding of the thermal properties of the device. Additionally, a set of extrapolation simulations has been performed illustrating the spontaneous formation of closed flux surfaces at high current amplification. Work supported by the US DOE.

Structural, electronic, elastic, and thermodynamic properties of CaSi, Ca2Si, and CaSi2 phases from first-principles calculations

NASA Astrophysics Data System (ADS)

Li, X. D.; Li, K.; Wei, C. H.; Han, W. D.; Zhou, N. G.

2018-06-01

The structural, electronic, elastic, and thermodynamic properties of CaSi, Ca2Si, and CaSi2 are systematically investigated by using first-principles calculations method based on density functional theory (DFT). The calculated formation enthalpies and cohesive energies show that CaSi2 possesses the greatest structural stability and CaSi has the strongest alloying ability. The structural stability of the three phases is compared according to electronic structures. Further analysis on electronic structures indicates that the bonding of these phases exhibits the combinations of metallic, covalent, and ionic bonds. The elastic constants are calculated, and the bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and anisotropy factor of polycrystalline materials are deduced. Additionally, the thermodynamic properties were theoretically predicted and discussed.

Interfacial Thickness Guidelines for SiC(Fiber)/SiC(Matrix) Composites

NASA Technical Reports Server (NTRS)

Hurst, Janet B.

1998-01-01

Researchers at the NASA Lewis Research Center have developed a guideline for the interface thickness necessary for SiC(Fiber)/SiC(Matrix) composites to demonstrate good composite properties. These composite materials have potential commercial applications for high-temperature structural components such as engine hot sections. Several samples of each were composed from three different small-diameter (less than 20 mm), polymer-derived SiC fibers that were woven into two-dimensional cloths and laid up as preforms. The preforms were treated with a chemical-vapor-infiltrated boron nitride layer as an interfacial coating on the fiber surfaces to provide the necessary debonding characteristics for successful composite behavior. Then, the preforms were filled with additional SiC as a matrix phase.

Development ceramic composites based on Al2O3, SiO2 and IG-017 additive

NASA Astrophysics Data System (ADS)

Kurovics, E.; Shmakova, A.; Kanev, B.; Gömze, L. A.

2017-02-01

Based on high purity alumina and quartz powders and IG-017 bio-original additives the authors have developed new ceramic composite materials for different industrial purposes. The main goal was to fine a material and morphological structures of high performance ceramic composites as frames for development complex materials for extreme consumptions in the future. For this the mixed powders of Al2O3 , SiO2 and IG-017 bio-original additive were uniaxially pressed at different compaction pressures into disc shapes and were sintered in electric kiln under air (1) and nitrogrn (2) atmosphere. The grain size distributions of the raw materials were determined by laser granulometry. There thermo-physical properties were also determined by derivatography. The prepared and sintered specimens were tested on geometrical sizes, microstructure and morphology by scanning electron microscopy, porosity and water absorption. In this work the authors present the results of their research and investigation.

Density-functional theory molecular dynamics simulations of a-HfO2/a-SiO2/SiGe and a-HfO2/a-SiO2/Ge with a-SiO2 and a-SiO suboxide interfacial layers

NASA Astrophysics Data System (ADS)

Chagarov, Evgueni A.; Kavrik, Mahmut S.; Fang, Ziwei; Tsai, Wilman; Kummel, Andrew C.

2018-06-01

Comprehensive Density-Functional Theory (DFT) Molecular Dynamics (MD) simulations were performed to investigate interfaces between a-HfO2 and SiGe or Ge semiconductors with fully-stoichiometric a-SiO2 or sub-oxide SiO interlayers. The electronic structure of the selected stacks was calculated with a HSE06 hybrid functional. Simulations were performed before and after hydrogen passivation of residual interlayer defects. For the SiGe substrate with Ge termination prior to H passivation, the stacks with a-SiO suboxide interlayer (a-HfO2/a-SiO/SiGe) demonstrate superior electronic properties and wider band-gaps than the stacks with fully coordinated a-SiO2 interlayers (a-HfO2/a-SiO2/SiGe). After H passivation, most of the a-HfO2/a-SiO2/SiGe defects are passivated. To investigate effect of random placement of Si and Ge atoms additional simulations with a randomized SiGe slab were performed demonstrating improvement of electronic structure. For Ge substrates, before H passivation, the stacks with a SiO suboxide interlayer (a-HfO2/a-SiO/Ge) also demonstrate wider band-gaps than the stacks with fully coordinated a-SiO2 interlayers (a-HfO2/a-SiO2/Ge). However, even for a-HfO2/a-SiO/Ge, the Fermi level is shifted close to the conduction band edge (CBM) consistent with Fermi level pinning. Again, after H passivation, most of the a-HfO2/a-SiO2/Ge defects are passivated. The stacks with fully coordinated a-SiO2 interlayers have much stronger deformation and irregularity in the semiconductor (SiGe or Ge) upper layers leading to multiple under-coordinated atoms which create band-edge states and decrease the band-gap prior to H passivation.

ZrO2 film interfaces with Si and SiO2

NASA Astrophysics Data System (ADS)

Lopez, C. M.; Suvorova, N. A.; Irene, E. A.; Suvorova, A. A.; Saunders, M.

2005-08-01

The interface formed by the thermal oxidation of sputter-deposited Zr metal onto Si(100)- and SiO2-coated Si(100) wafers was studied in situ and in real time using spectroscopic ellipsometry (SE) in the 1.5-4.5 photon energy range and mass spectrometry of recoiled ions (MSRI). SE yielded optical properties for the film and interface and MSRI yielded film and interface composition. An optical model was developed and verified using transmission electron microscopy. Interfacial reaction of the ZrO2 was observed for both substrates, with more interaction for Si substrates. Equivalent oxide thicknesses and interface trap levels were determined on capacitors with lower trap levels found on samples with a thicker SiO2 underlayer. In addition to the optical properties for the intermixed interface layer, the optical properties for Zr metal and unreacted ZrO2 are also reported.

Structure and soft magnetic properties of Fe-Si-B-P-Cu nanocrystalline alloys with minor Mn addition

NASA Astrophysics Data System (ADS)

Jia, Xingjie; Li, Yanhui; Wu, Licheng; Zhang, Wei

2018-05-01

Addition of minor Mn effectively improves the amorphous-forming ability and thermal stability of the Fe85Si2B8P4Cu1 alloy. With increasing the Mn content from 0 to 3 at.%, the critical thickness for amorphous formation and onset temperature of the primary crystallization increase from 14 μm and 659 K to 27 μm and 668 K, respectively. The fine nanocrystalline structure with α-Fe grains in size (D) of < 20 nm was obtained for the annealed amorphous alloys, which show excellent soft magnetic properties. The alloying of Mn reduces the coercivity (Hc) by decreasing the D value and widens the optimum annealing temperature range for obtaining low Hc, although the saturation magnetic flux density (Bs) is decreased slightly. The Fe83Mn2Si2B8P4Cu1 nanocrystalline alloy possesses fine structure with a D of ˜17.5 nm, and exhibits a high Bs of ˜1.75 T and a low Hc of ˜5.9 A/m. The mechanism related to the alloying effects on the structure and magnetic properties was discussed in term of the crystallization activation energy.

Effect of High Si Content on U3Si2 Fuel Microstructure

NASA Astrophysics Data System (ADS)

Rosales, Jhonathan; van Rooyen, Isabella J.; Meher, Subhashish; Hoggan, Rita; Parga, Clemente; Harp, Jason

2018-02-01

The development of U3Si2 as an accident-tolerant nuclear fuel has gained research interest because of its promising high uranium density and improved thermal properties. In the present study, three samples of U3Si2 fuel with varying silicon content have been fabricated by a conventional powder metallurgical route. Microstructural characterization via scanning and transmission electron microscopy reveals the presence of other stoichiometry of uranium silicide such as USi and UO2 in both samples. The detailed phase analysis by x-ray diffraction shows the presence of secondary phases, such as USi, U3Si, and UO2. The samples with higher concentrations of silicon content of 7.5 wt.% display additional elemental Si. These samples also possess an increased amount of the USi phase as compared to that in the conventional sample with 7.3 wt.% silicon. The optimization of U3Si2 fuel performance through the understanding of the role of Si content on its microstructure has been discussed.

Sr-Al-Si co-segregated regions in eutectic Si phase of Sr-modified Al-10Si alloy.

PubMed

Timpel, M; Wanderka, N; Schlesiger, R; Yamamoto, T; Isheim, D; Schmitz, G; Matsumura, S; Banhart, J

2013-09-01

The addition of 200 ppm strontium to an Al-10 wt% Si casting alloy changes the morphology of the eutectic silicon phase from coarse plate-like to fine fibrous networks. In order to clarify this modification mechanism the location of Sr within the eutectic Si phase has been investigated by a combination of high-resolution methods. Whereas three-dimensional atom probe tomography allows us to visualise the distribution of Sr on the atomic scale and to analyse its local enrichment, transmission electron microscopy yields information about the crystallographic nature of segregated regions. Segregations with two kinds of morphologies were found at the intersections of Si twin lamellae: Sr-Al-Si co-segregations of rod-like morphology and Al-rich regions of spherical morphology. Both are responsible for the formation of a high density of multiple twins and promote the anisotropic growth of the eutectic Si phase in specific crystallographic directions during solidification. The experimental findings are related to the previously postulated mechanism of "impurity induced twinning". Copyright © 2012 Elsevier B.V. All rights reserved.

Friction and Wear Properties of CrSiCN/SiC Tribopairs in Water Lubrication

NASA Astrophysics Data System (ADS)

Wu, Zhiwei; Zhou, Fei; Wang, Qianzhi

2018-05-01

CrSiCN coatings (3.4 at.% Si) were prepared on 316L stainless steels using unbalanced magnetron sputtering. According to the analysis results of x-ray diffractometer and x-ray photoelectrons spectroscopy, silicon in CrSiCN coatings mainly presented in the amorphous forms of a-SiN, a-SiCN and a-SiC. The hardness and Young's modulus of CrSiN coatings were 19.4 ± 0.6 and 306.1 ± 5.9 GPa, respectively. In addition, the ball-on-disk sliding tests of CrSiCN/SiC tribopairs were performed in distilled water at varying velocities (0.1-0.5 m/s) and loads (2-12 N). The friction coefficient of tribopairs presented a decreasing trend with respect to velocity at low applied loads (≤ 4 N). To be specific, the low friction coefficient of 0.05-0.14 accompanied with polished wear scar was obtained at high velocities and low loads. Finally, the wear mechanism map of CrSiCN/SiC tribopairs was proposed based on a combination of friction coefficient, wear scar morphology and wear rates of tribopairs.

Influences of Na2O and K2O Additions on Electrical Conductivity of CaO-MgO-Al2O3-SiO2 Melts

NASA Astrophysics Data System (ADS)

Zhang, Guo-Hua; Zheng, Wei-Wei; Chou, Kuo-Chih

2017-04-01

The present study investigated the influences of Na2O and K2O additions on electrical conductivity of blast furnace type CaO-MgO-Al2O3-SiO2 melts by the four-electrode method. Both the single addition of Na2O or K2O and the double additions of Na2O and K2O were studied. It was found that electrical conductivity monotonously increased as the amount of Na2O addition was gradually increased, whereas, when K2O was added, there was a continuous decrease of electrical conductivity. With melts containing both Na2O and K2O, electrical conductivity first decreased but then increased when Na2O was gradually substituted for K2O while keeping the molar fractions of other components constant. In other words, the mixed-alkali effect took place in CaO-Mg-Al2O3-SiO2-ΣR2O melts.

Emerging technologies in Si active photonics

NASA Astrophysics Data System (ADS)

Wang, Xiaoxin; Liu, Jifeng

2018-06-01

Silicon photonics for synergistic electronic–photonic integration has achieved remarkable progress in the past two decades. Active photonic devices, including lasers, modulators, and photodetectors, are the key challenges for Si photonics to meet the requirement of high bandwidth and low power consumption in photonic datalinks. Here we review recent efforts and progress in high-performance active photonic devices on Si, focusing on emerging technologies beyond conventional foundry-ready Si photonics devices. For emerging laser sources, we will discuss recent progress towards efficient monolithic Ge lasers, mid-infrared GeSn lasers, and high-performance InAs quantum dot lasers on Si for data center applications in the near future. We will then review novel modulator materials and devices beyond the free carrier plasma dispersion effect in Si, including GeSi and graphene electro-absorption modulators and plasmonic-organic electro-optical modulators, to achieve ultralow power and high speed modulation. Finally, we discuss emerging photodetectors beyond epitaxial Ge p–i–n photodiodes, including GeSn mid-infrared photodetectors, all-Si plasmonic Schottky infrared photodetectors, and Si quanta image sensors for non-avalanche, low noise single photon detection and photon counting. These emerging technologies, though still under development, could make a significant impact on the future of large-scale electronicSilicon photonics for synergistic electronic-photonic integration has achieved remarkable progress in the past two decades. Active photonic devices, including lasers, modulators, and photodetectors, are the key challenges for Si photonics to meet the requirement of high bandwidth and low power consumption in photonic datalinks. Here we review recent efforts and progress in high-performance active photonic devices on Si, focusing on emerging technologies beyond conventional foundry-ready Si photonics devices. For emerging laser sources, we will discuss recent

SiC Nanowires Synthesized by Rapidly Heating a Mixture of SiO and Arc-Discharge Plasma Pretreated Carbon Black.

PubMed

Wang, Feng-Lei; Zhang, Li-Ying; Zhang, Ya-Fei

2008-11-22

SiC nanowires have been synthesized at 1,600 degrees C by using a simple and low-cost method in a high-frequency induction furnace. The commercial SiO powder and the arc-discharge plasma pretreated carbon black were mixed and used as the source materials. The heating-up and reaction time is less than half an hour. It was found that most of the nanowires have core-shell SiC/SiO(2) nanostructures. The nucleation, precipitation, and growth processes were discussed in terms of the oxide-assisted cluster-solid mechanism.

SiC Nanowires Synthesized by Rapidly Heating a Mixture of SiO and Arc-Discharge Plasma Pretreated Carbon Black

PubMed Central

2009-01-01

SiC nanowires have been synthesized at 1,600 °C by using a simple and low-cost method in a high-frequency induction furnace. The commercial SiO powder and the arc-discharge plasma pretreated carbon black were mixed and used as the source materials. The heating-up and reaction time is less than half an hour. It was found that most of the nanowires have core-shell SiC/SiO2nanostructures. The nucleation, precipitation, and growth processes were discussed in terms of the oxide-assisted cluster-solid mechanism. PMID:20596456

Optimization of Silicon parameters as a betavoltaic battery: Comparison of Si p-n and Ni/Si Schottky barrier

NASA Astrophysics Data System (ADS)

Rahmani, Faezeh; Khosravinia, Hossein

2016-08-01

Theoretical studies on the optimization of Silicon (Si) parameters as the base of betavoltaic battery have been presented using Monte Carlo simulations and the state equations in semiconductor to obtain maximum power. Si with active area of 1 cm2 has been considered in p-n junction and Schottky barrier structure to collect the radiation induced-charge from 10 mCi cm-2 of Nickle-63 (63Ni) Source. The results show that the betavoltaic conversion efficiency in the Si p-n structure is about 2.7 times higher than that in the Ni/Si Schottky barrier structure.

Effects of addition of supramolecular assembly on the anatase nanocrystalline precipitation of sol-gel derived SiO2-TiO2 coating films by hot-water treatment.

PubMed

Katagiri, Kiyofumi; Harada, Genki; Matsuda, Atsunori; Kogure, Toshihiro; Muto, Hiroyuki; Sakai, Mototsugu

2006-06-01

Effects of the addition of a supramolecular assembly of cetyltrimethylammonium bromide in SiO2-TiO2 gel films on the formation of anatase type TiO2 nanocrystals with hot-water treatment were investigated. Anatase nanocrystals were formed in the whole SiO2-TiO2 gel films with the addition of cetyltrimethylammonium bromide by the treatment, whereas the nanocrystals were formed only on the film surface in the case of gel films without cetyltrimethylammonium bromide. Cetyltrimethylammonium bromide molecules in the SiO2-TiO2 gel films were completely removed by the hot-water treatment and the following UV irradiation. In the usual procedure for preparation of porous materials, the removal of template molecular assemblies required high temperature treatment over 400 degrees C. In this system, all the processes were performed at temperatures less than 100 degrees C. Additionally, the porous structure produced by the removal of micellar assembly allowed anatase nanocrystals to be formed inside the films. Therefore, the method presented in this work provides us with the novel photocatalyst coatings of porous membrane with highly-dispersed TiO2 nanocrystals via low temperature process.

Monitoring Observatinos of H2O and SiO Masers Toward Post-AGB Stars

NASA Astrophysics Data System (ADS)

Kim, Jaeheon; Cho, Se-Hyung; Yoon, Dong-Hwan

2016-12-01

We present the results of simultaneous monitoring observations of H_2O 6_{1,6}-5_{2,3} (22 GHz) and SiO J=1-0, 2-1, 3-2 maser lines (43, 86, 129 GHz) toward five post-AGB (candidate) stars, using the 21-m single-dish telescopes of the Korean VLBI Network. Depending on the target objects, 7 - 11 epochs of data were obtained. We detected both H_2O and SiO maser lines from four sources: OH16.1-0.3, OH38.10-0.13, OH65.5+1.3, and IRAS 19312+1950. We could not detect H_2O maser emission toward OH13.1+5.1 between the late OH/IR and post-AGB stage. The detected H_2O masers show typical double-peaked line profiles. The SiO masers from four sources, except IRAS 19312+1950, show the peaks around the stellar velocity as a single peak, whereas the SiO masers from IRAS 19312+1950 occur above the red peak of the H_2O maser. We analyzed the properties of detected maser lines, and investigated their evolutionary state through comparison with the full widths at zero power. The distribution of observed target sources was also investigated in the IRAS two-color diagram in relation with the evolutionary stage of post-AGB stars. From our analyses, the evolutionary sequence of observed sources is suggested as OH65.5+1.3 → OH13.1+5.1 → OH16.1-0.3 → OH38.10-0.13, except for IRAS 19312+1950. In addition, OH13.1+5.1 from which the H_2O maser has not been detected is suggested to be on the gateway toward the post-AGB stage. With respect to the enigmatic object, IRAS 19312+1950, we could not clearly figure out its nature. To properly explain the unusual phenomena of SiO and H_2O masers, it is essential to establish the relative locations and spatial distributions of two masers using VLBI technique. We also include the 1.2 - 160 μm spectral energy distribution using photometric data from the following surveys: 2MASS, WISE, MSX, IRAS, and AKARI (IRC and FIS). In addition, from the IRAS LRS spectra, we found that the depth of silicate absorption features shows significant variations

Precise Perforation and Scalable Production of Si Particles from Low-Grade Sources for High-Performance Lithium Ion Battery Anodes.

PubMed

Zong, Linqi; Jin, Yan; Liu, Chang; Zhu, Bin; Hu, Xiaozhen; Lu, Zhenda; Zhu, Jia

2016-11-09

Alloy anodes, particularly silicon, have been intensively pursued as one of the most promising anode materials for the next generation lithium-ion battery primarily because of high specific capacity (>4000 mAh/g) and elemental abundance. In the past decade, various nanostructures with porosity or void space designs have been demonstrated to be effective to accommodate large volume expansion (∼300%) and to provide stable solid electrolyte interphase (SEI) during electrochemical cycling. However, how to produce these building blocks with precise morphology control at large scale and low cost remains a challenge. In addition, most of nanostructured silicon suffers from poor Coulombic efficiency due to a large surface area and Li ion trapping at the surface coating. Here we demonstrate a unique nanoperforation process, combining modified ball milling, annealing, and acid treating, to produce porous Si with precise and continuous porosity control (from 17% to 70%), directly from low cost metallurgical silicon source (99% purity, ∼ $1/kg). The produced porous Si coated with graphene by simple ball milling can deliver a reversible specific capacity of 1250 mAh/g over 1000 cycles at the rate of 1C, with Coulombic efficiency of first cycle over 89.5%. The porous networks also provide efficient ion and electron pathways and therefore enable excellent rate performance of 880 mAh/g at the rate of 5C. Being able to produce particles with precise porosity control through scalable processes from low-grade materials, it is expected that this nanoperforation may play a role in the next generation lithium ion battery anodes, as well as many other potential applications such as optoelectronics and thermoelectrics.

The Stellar Imager (SI) Project: A Deep Space UV/Optical Interferometer (UVOI) to Observe the Universe at 0.1 Milli-Arcsec Angular Resolution

NASA Technical Reports Server (NTRS)

Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

2008-01-01

The Stellar Imager (SI) is a space-based, UV/ Optical Interferometer (UVOI) designed to enable 0.1 milliarcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI's science focuses on the role of magnetism in the Universe and will revolutionize our understanding, of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes, such as accretion, in the Universe. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI is a "Flagship and Landmark Discovery Mission" in the 2005 Heliophysics Roadmap and a potential implementation of the UVOI in the 2006 Science Program for NASA's Astronomy and Physics Division. We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this missin. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/.

Fracture mode, microstructure and temperature-dependent elastic moduli for thermoelectric composites of PbTe-PbS with SiC nanoparticle additions

NASA Astrophysics Data System (ADS)

Ni, Jennifer E.; Case, Eldon D.; Schmidt, Robert D.; Wu, Chun-I.; Hogan, Timothy P.; Trejo, Rosa M.; Lara-Curzio, Edgar; Kanatzidis, Mercouri G.

2013-12-01

Twenty-six (Pb0.95Sn0.05Te)0.92(PbS)0.08-0.055% PbI2-SiC nanoparticle (SiCnp) composite thermoelectric specimens were either hot pressed or pulsed electric current sintered (PECS). Bloating (a thermally induced increase in porosity, P, for as-densified specimens) was observed during annealing at temperatures >603 K for hot-pressed specimens and PECS-processed specimens from wet milled powders, but in contrast seven out of seven specimens densified by PECS from dry milled powders showed no observable bloating following annealing at temperatures up to 936 K. In this study, bloating in the specimens was accessed via thermal annealing induced changes in (i) porosity measured by scanning electron microscopy on fractured specimen surfaces, (ii) specimen volume and (iii) elastic moduli. The moduli were measured by resonant ultrasound spectroscopy. SiCnp additions (1-3.5 vol.%) changed the fracture mode from intergranular to transgranular, inhibited grain growth, and limited bloating in the wet milled PECS specimens. Inhibition of bloating likely occurs due to cleaning of contamination from powder particle surfaces via PECS processing which has been reported previously in the literature.

40 CFR 60.4247 - What parts of the mobile source provisions apply to me if I am a manufacturer of stationary SI...

Code of Federal Regulations, 2010 CFR

2010-07-01

... 40 Protection of Environment 6 2010-07-01 2010-07-01 false What parts of the mobile source provisions apply to me if I am a manufacturer of stationary SI internal combustion engines or a manufacturer of equipment containing such engines? 60.4247 Section 60.4247 Protection of Environment ENVIRONMENTAL...

The Ge/Si ratio quantifies the role of recycled crust in the generation of MORBs

NASA Astrophysics Data System (ADS)

Yang, S.; Humayun, M.; Salters, V. J. M.

2017-12-01

Global MORBs cover a broad spectrum of incompatible element compositions from depleted [(La/Sm)N < 0.5] to enriched [(La/Sm)N 0.5-2]. Two explanations for the origin of the enriched mantle sources of E-MORBs from ridge segments not associated with plumes have been proposed: (1) re-fertilization of Depleted Mantle (DM) by infiltration of low-degree melts (<1%) from subducted crust, or (2) by entrainment of solid recycled crust in the Depleted Mantle (DM). Whether pyroxenite contributes melt to E-MORB can be resolved by chemically distinguishing between partial melts of a peridotite source vs. those of a lithologically heterogeneous source of peridotite and pyroxenite. In this study, we exploit the mineralogical preferences of elements like Ge and Si to distinguish melts formed from peridotite or pyroxenite. In-situ analyses of 60 elements in 319 MORB glasses from north (10-36 °N) Mid-Atlantic Ridge (MAR) and Mid-Cayman Rise were performed by LA-ICP-MS. Use of a large laser spot size (150 μm) and high repetition rate (50 Hz) yielded a low blank correction (< 5%) for Ge, and high external precision for the Ge/Si ratio (± 3%, 1σ) in MORB glasses. E-MORBs (6.4±0.2) are systematically lower in Ge/Si than D-MORBs (7.2±0.2), while N-MORBs fall in between and are not fully resolved from either D- or E-MORB. Based on experimental Ds, partial melts from pyroxenites are always lower in Ge/Si than partial melts from peridotites because Ge is more compatible in garnet and clinopyroxene than in olivine [1]. E-MORBs also have lower Sc abundances (37 vs. 43 ppm) but slightly higher Fe/Mn ratios (55 vs. 53) than D-MORBs, and lower La/Nb (0.6 vs. 1-2) and Sr/Nb (<20 vs. >40), consistent with addition of 27% pyroxenite-derived melts to a D-MORB-like composition. This requires that the amount of solid recycled garnet pyroxenite in a peridotite source is 12%. The Ge/Si ratio is a new tool that effectively discriminates between melts derived from peridotite sources and melts

Scattering mechanisms in shallow undoped Si/SiGe quantum wells

DOE PAGES

Laroche, Dominique; Huang, S. -H.; Nielsen, Erik; ...

2015-10-07

We report the magneto-transport study and scattering mechanism analysis of a series of increasingly shallow Si/SiGe quantum wells with depth ranging from ~ 100 nm to ~ 10 nm away from the heterostructure surface. The peak mobility increases with depth, suggesting that charge centers near the oxide/semiconductor interface are the dominant scattering source. The power-law exponent of the electron mobility versus density curve, μ ∝ n α, is extracted as a function of the depth of the Si quantum well. At intermediate densities, the power-law dependence is characterized by α ~ 2.3. At the highest achievable densities in the quantummore » wells buried at intermediate depth, an exponent α ~ 5 is observed. Lastly, we propose and show by simulations that this increase in the mobility dependence on the density can be explained by a non-equilibrium model where trapped electrons smooth out the potential landscape seen by the two-dimensional electron gas.« less

NHC→SiCl4 : an ambivalent carbene-transfer reagent.

PubMed

Böttcher, Tobias; Steinhauer, Simon; Lewis-Alleyne, Lesley C; Neumann, Beate; Stammler, Hans-Georg; Bassil, Bassem S; Röschenthaler, Gerd-Volker; Hoge, Berthold

2015-01-07

The addition of BCl3 to the carbene-transfer reagent NHC→SiCl4 (NHC=1,3-dimethylimidazolidin-2-ylidene) gave the tetra- and pentacoordinate trichlorosilicon(IV) cations [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) with tetrachloroborate as counterion. This is in contrast to previous reactions, in which NHC→SiCl4 served as a transfer reagent for the NHC ligand. The addition of BF3 ⋅OEt2 , on the other hand, gave NHC→BF3 as the product of NHC transfer. In addition, the highly Lewis acidic bis(pentafluoroethyl)silane (C2 F5 )2 SiCl2 was treated with NHC→SiCl4 . In acetonitrile, the cationic silicon(IV) complexes [(NHC)SiCl3 ](+) and [(NHC)2 SiCl3 ](+) were detected with [(C2 F5 )SiCl3 ](-) as counterion. A similar result was already reported for the reaction of NHC→SiCl4 with (C2 F5 )2 SiH2 , which gave [(NHC)2 SiCl2 H][(C2 F5 )SiCl3 ]. If the reaction medium was changed to dichloromethane, the products of carbene transfer, NHC→Si(C2 F5 )2 Cl2 and NHC→Si(C2 F5 )2 ClH, respectively, were obtained instead. The formation of the latter species is a result of chloride/hydride metathesis. These compounds may serve as valuable precursors for electron-poor silylenes. Furthermore, the reactivity of NHC→SiCl4 towards phosphines is discussed. The carbene complex NHC→PCl3 shows similar reactivity to NHC→SiCl4 , and may even serve as a carbene-transfer reagent as well. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

III-nitride nanowire LEDs and diode lasers: monolithic light sources on (001) Si emitting in the 600-1300nm range

NASA Astrophysics Data System (ADS)

Bhattacharya, P.; Hazari, A.; Jahangir, S.

2018-02-01

GaN-based nanowire heterostructure arrays epitaxially grown on (001)Si substrates have unique properties and present the potential to realize useful devices. The active light-emitting region in the nanowire heterostructures are usually InGaN disks, whose composition can be varied to tune the emission wavelength. We have demonstrated light emitting diodes and edgeemitting diode lasers with power outputs 10mW with emission in the 600-1300nm wavelength range. These light sources are therefore useful for a variety of applications, including silicon photonics. Molecular beam epitaxial growth of the nanowire heterostructure arrays on (001)Si substrates and the characteristics of 1.3μm nanowire array edge emitting lasers, guided wave photodiodes and a monolithic photonic integrated circuit designed for 1.3μm operation are described.

Effect of SiC particle size on the microstructure and properties of cold-sprayed Al/SiCp composite coating

NASA Astrophysics Data System (ADS)

Yu, Min; Hua, Junwei

2017-07-01

The Al5056/SiC composite coatings were prepared by cold spraying. Experimental results show that the SiC content in the composite coating deposited with the SiC powder having an average size of 67 μm (Al5056/SiC-67) is similar to that deposited with the SiC powder having an average size of 27 μm (Al5056/SiC-27). The microhardness and cohesion strength of Al5056/SiC-67 coating are higher than those of the Al5056/SiC-27 coating. In addition, the Al5056/SiC-67 coating having a superior wear resistance because of the coarse SiC powder with a superior kinetic energy contributes to the deformation resistance of the matrix Al5056 particles.

Reduction mechanisms of additives on Si anodes of Li-ion batteries.

PubMed

Martínez de la Hoz, Julibeth M; Balbuena, Perla B

2014-08-28

Solid-electrolyte interphase (SEI) layers are films deposited on the surface of Li-ion battery electrodes during battery charge and discharge processes. They are due to electrochemical instability of the electrolyte which causes electron transfer from (to) the anode (cathode) surfaces. The films could have a protective passivating role and therefore understanding the detailed reduction (oxidation) processes is essential. Here density functional theory and ab initio molecular dynamics simulations are used to investigate the reduction mechanisms of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) on lithiated silicon surfaces. These species are frequently used as "additives" to improve the SEI properties. It is found that on lithiated Si anodes (with low to intermediate degrees of lithiation) VC may be reduced via a 2e(-) mechanism yielding an opened VC(2-) anion. At higher degrees of lithiation, such a species receives two extra electrons from the surface resulting in an adsorbed CO(2-)(ads) anion and a radical anion ˙OC2H2O(2-). Additionally, in agreement with experimental observations, it is shown that CO2 can be generated from reaction of VC with the CO3(2-)anion, a product of the reduction of the main solvent, ethylene carbonate (EC). On the other hand, FEC reduction on LixSiy surfaces is found to be independent of the degree of lithiation, and occurs through three mechanisms. One of them leads to an adsorbed VC(2-) anion upon release from the FEC molecule and adsorption on the surface of F(-) and one H atom. Thus in some cases, the reduction of FEC may lead to the exact same reduction products as that of VC, which explains similarities in SEI layers formed in the presence of these additives. However, FEC may be reduced via two other multi-electron transfer mechanisms that result in formation of either CO2(2-), F(-), and ˙CH2CHO(-) or CO(2-), F(-), and ˙OCH2CHO(-). These alternative reduction products may oligomerize and form SEI layers with

Antireflective hydrophobic si subwavelength structures using thermally dewetted Ni/SiO2 nanomask patterns.

PubMed

Joo, Dong Hyuk; Leem, Jung Woo; Yu, Jae Su

2011-11-01

We report the disordered silicon (Si) subwavelength structures (SWSs), which are fabricated with the use of inductively coupled plasma (ICP) etching in SiCl4 gas using nickel/silicon dioxide (Ni/SiO2) nanopattens as the etch mask, on Si substrates by varying the etching parameters for broadband antireflective and self-cleaning surfaces. For the fabricated Si SWSs, the antireflection characteristics are experimentally investigated and a theoretical analysis is made based on the rigorous coupled-wave analysis method. The desirable dot-like Ni nanoparticles on SiO2/Si substrates are formed by the thermal dewetting process of Ni films at 900 degrees C. The truncated cone shaped Si SWS with a high average height of 790 +/- 23 nm, which is fabricated by ICP etching with 5 sccm SiCl4 at 50 W RF power with additional 200 W ICP power under 10 mTorr process pressure, exhibits a low average reflectance of approximately 5% over a wide wavelength range of 450-1050 nm. The water contact angle of 110 degrees is obtained, indicating a hydrophobic surface. The calculated reflectance results are also reasonably consistent with the experimental data.

Chemical reactivity of SiC fibre-reinforced SiC with beryllium and lithium ceramic breeder materials

NASA Astrophysics Data System (ADS)

Kleykamp, H.

2000-12-01

SiC fibre-reinforced SiC fabrics (f-SiC/SiC) are considered for structural materials of advanced fusion blanket concepts. Priority tasks are compatibility studies of SiC with Li breeder ceramics and the Be neutron multiplier. Isothermal and anisothermal powder reactions by DTA up to 1220°C were examined between Li 4SiO 4, Li 2ZrO 3 and Li 2TiO 3, respectively, and SiC and SiC/SiO 2 mixtures, respectively. The SiC/SiO 2 mixture simulated the chemical state of Nicalon fibres. Solid state reactions between SiC and Be pellets were studied by capsule experiments. The reaction products Be 2C and Si were observed between the initial phases after annealing at 800°C and 900°C. A parabolic time law with a chemical diffusion coefficient D˜=2.6×10 -15 m 2/s of Be in the products was deduced at 900°C. Additional oxygen released from SiO 2 as a component of the simulated fibres oxidised the reaction products via the gas phase by formation of a Be 2SiO 4 layer. All reactions are kinetically hindered below 700°C.

Novel approach for III-N on Si (111) templates fabrication by low-temperature PA MBE using porous Si layer

NASA Astrophysics Data System (ADS)

Zolotukhin, D.; Seredin, P.; Lenshin, A.; Goloshchapov, D.; Mizerov, A.

2017-11-01

We report on successful growth of GaN nanorods by low-temperature plasma-assisted molecular beam epitaxy on a Si(111) substrate with and without preformed thin porous Si layer (por-Si). The deposited GaN initially forms islands which act as a seed for the wires. Porous structure of the por-Si layer helps to control nucleation islands sizes and achieve homogeneous distribution of the nanorods diameters. In addition 850 nm-thick crack-free GaN layer was formed on Si(111) substrate with preformed por-Si layer.

Effects of SiC whiskers and particles on precipitation in aluminum matrix composites

NASA Astrophysics Data System (ADS)

Papazian, John M.

1988-12-01

The age-hardening precipitation reactions in aluminum matrix composites reinforced with discontinuous SiC were studied using a calorimetric technique. Composites fabricated with 2124, 2219, 6061, and 7475 alloy matrices were obtained from commercial sources along with unreinforced control materials fabricated in a similar manner. The 7475 materials were made by a casting process while the others were made by powder metallurgy: the SiC reinforcement was in the form of whiskers or particulate. It was found that the overall age-hardening sequence of the alloy was not changed by the addition of SiC, but that the volume fractions of various phases and the precipitation kinetics were substantially modified. Precipitation and dissolution kinetics were generally accelerated. A substantial portion of this acceleration was found to be due to the powder metallurgy process employed to make the composites, but the formation kinetics of some particular precipitate phases were also strongly affected by the presence of SiC. It was observed that the volume fraction of GP zones able to form in the SiC containing materials was significantly reduced. The presence of SiC particles also caused normally quench insensitive materials such as 6061 to become quench sensitive. The microstructural origins of these effects are discussed.

Study of astrophysically important resonant states in 26Si by the 28Si(4He,6He)26Si reaction

NASA Astrophysics Data System (ADS)

Kwon, Young Kwan; Lee, C. S.; Moon, J. Y.; Lee, J. H.; Kim, J. Y.; Kubono, S.; Iwasa, N.; Inafiki, K.; Yamaguchi, H.; He, J. J.; Saito, A.; Wakabayashi, Y.; Fukijawa, H.; Amadio, G.; Khiem, L. H.; Tanaka, M.; Chen, A.; Kato, S.

PoS(NIC-IX)024 , b, H. Yamaguchia, J. J. Hea , A. Saitoa , Y. Wakabayashia, H. Fujikawaa, G. The emission of 1.809 MeV gamma-ray from the first excited state of 26 Mg followed by beta- decay of 26 Al in its ground state (denoted as 26 Alg.s. ) has been identified by gamma-ray telescopes such the Compton Gamma-Ray Observatory (CGRO) [1]. To resolve controversy over the pos- sible sources of the observational 1.809 MeV gamma-rays, one needs accurate knowledge of the production rate of 26 Al. The 25 Al(p,γ)26Si reaction which is the competition reaction for produc- tion of 26 Alg.s. is one of the important subjects to be investigated. In this work, the astrophysically important 26 Si states above the proton threshold were studied via the 28 Si(4 He,6 He)26 Si reaction. We have preformed an angular distribution measurement using the high resolution QDD spectro- graph (PA) at Center for Nuclear Study (CNS), University of Tokyo. The experimental results and data analysis will be presented.

Pest resistant MoSi2-based materials containing in-situ grown .beta.-Si3N4whiskers

NASA Technical Reports Server (NTRS)

Hebsur, Mohan G. (Inventor)

2001-01-01

A MoSi.sub.2 pest resistant material includes in-situ grown .beta.-Si.sub.3 N.sub.4 whiskers. In addition to excellent pest resistance, the material provides a lower coefficient of thermal expansion for better match with continuous reinforcing fibers such as SiC fibers. A two stage heating and pressing production technique enables lower temperature processing with substantially full densification.

Pest resistant MoSi2-based materials containing in-situ grown .beta.-Si3N4 whiskers

NASA Technical Reports Server (NTRS)

Hebsur, Mohan G. (Inventor)

2002-01-01

A MoSi.sub.2 pest resistant material includes in-situ grown .beta.-Si.sub.3 N.sub.4 whiskers. In addition to excellent pest resistance, the material provides a lower coefficient of thermal expansion for better match with continuous reinforcing fibers such as SiC fibers. A two stage heating and pressing production technique enables lower temperature processing with substantially full densification.

Effect of Alloying Elements on Nb-Rich Portion of Nb-Si-X Ternary Systems and In Situ Crack Observation of Nb-Si-Based Alloys

NASA Astrophysics Data System (ADS)

Miura, Seiji; Hatabata, Toru; Okawa, Takuya; Mohri, Tetsuo

2014-03-01

To find a new route for microstructure control and to find additive elements beneficial for improving high-temperature strength, a systematic investigation is performed on hypoeutectic Nb-15 at. pct Si-X ternary alloys containing a transition element, Fe, Co, Ni, Cu, Ru, Rh, Pd, Re, Os, Ir, Pt, or Au. Information on phase equilibrium is classified in terms of phase stability of silicide phases, α Nb5Si3, Nb4SiX, and Nb3Si, and the relationship between microstructure and mechanical properties both at room temperature and high temperature is investigated. All the additive elements are found to stabilize either α Nb5Si3 or Nb4SiX but destabilize Nb3Si. A microstructure of Nbss/α Nb5Si3 alloy composed of spheroidized α Nb5Si3 phase embedded in the Nbss matrix is effective for toughening, regardless of the initial as-cast microstructure. Also the plastic deformation of Nbss dendrites may effectively suppress the propagation of longer cracks. High-temperature strength of alloys is governed by the deformation of Nbss phase and increases with higher melting point additives.

Possibilities for LWIR detectors using MBE-grown Si(/Si(1-x)Ge(x) structures

NASA Technical Reports Server (NTRS)

Hauenstein, Robert J.; Miles, Richard H.; Young, Mary H.

1990-01-01

Traditionally, long wavelength infrared (LWIR) detection in Si-based structures has involved either extrinsic Si or Si/metal Schottky barrier devices. Molecular beam epitaxially (MBE) grown Si and Si/Si(1-x)Ge(x) heterostructures offer new possibilities for LWIR detection, including sensors based on intersubband transitions as well as improved conventional devices. The improvement in doping profile control of MBE in comparison with conventional chemical vapor deposited (CVD) Si films has resulted in the successful growth of extrinsic Si:Ga, blocked impurity-band conduction detectors. These structures exhibit a highly abrupt step change in dopant profile between detecting and blocking layers which is extremely difficult or impossible to achieve through conventional epitaxial growth techniques. Through alloying Si with Ge, Schottky barrier infrared detectors are possible, with barrier height values between those involving pure Si or Ge semiconducting materials alone. For both n-type and p-type structures, strain effects can split the band edges, thereby splitting the Schottky threshold and altering the spectral response. Measurements of photoresponse of n-type Au/Si(1-x)Ge(x) Schottky barriers demonstrate this effect. For intersubband multiquntum well (MQW) LWIR detection, Si(1-x)Ge(x)/Si detectors grown on Si substrates promise comparable absorption coefficients to that of the Ga(Al)As system while in addition offering the fundamental advantage of response to normally incident light as well as the practical advantage of Si-compatibility. Researchers grew Si(1-x)Ge(x)/Si MQW structures aimed at sensitivity to IR in the 8 to 12 micron region and longer, guided by recent theoretical work. Preliminary measurements of n- and p-type Si(1-x)Ge(x)/Si MQW structures are given.

NIMROD Simulations of the HIT-SI and HIT-SI3 Devices

NASA Astrophysics Data System (ADS)

Morgan, Kyle; Jarboe, Tom; Hossack, Aaron; Chandra, Rian; Everson, Chris

2017-10-01

The Helicity Injected Torus with Steady Inductive helicity injection (HIT-SI) experiment uses a set of inductively driven helicity injectors to apply non-axisymmetric current drive on the edge of the plasma, driving an axisymmetric spheromak equilibrium in a central confinement volume. Significant improvements have been made to extended MHD modeling of HIT-SI, with both the resolution of disagreement at high injector frequencies in HIT-SI in addition to successes with the new upgraded HIT-SI3 device. Previous numerical studies of HIT-SI, using a zero-beta eMHD model, focused on operations with a drive frequency of 14.5 kHz, and found reduced agreement with both the magnetic profile and current amplification at higher frequencies (30-70 kHz). HIT-SI3 has three helicity injectors which are able to operate with different mode structures of perturbations through the different relative temporal phasing of the injectors. Simulations that allow for pressure gradients have been performed in the parameter regimes of both devices using the NIMROD code and show improved agreement with experimental results, most notably capturing the observed Shafranov-shift due to increased beta observed at higher finj in HIT-SI and the variety of toroidal perturbation spectra available in HIT-SI3. This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under Award Number DE-FG02- 96ER54361.

Intermixing and thermal oxidation of ZrO2 thin films grown on a-Si, SiN, and SiO2 by metallic and oxidic mode magnetron sputtering

NASA Astrophysics Data System (ADS)

Coloma Ribera, R.; van de Kruijs, R. W. E.; Sturm, J. M.; Yakshin, A. E.; Bijkerk, F.

2017-03-01

The initial growth of DC sputtered ZrO2 on top of a-Si, SiN, and SiO2 layers has been studied by in vacuo high-sensitivity low energy ion scattering for two gas deposition conditions with different oxygen contents (high-O and low-O conditions). This unique surface sensitive technique allowed the determination of surface composition and thicknesses required to close the ZrO2 layer on all three substrates for both conditions. The ZrO2 layer closes similarly on all substrates due to more favorable enthalpies of formation for ZrO2 and ZrSiO4, resulting in passivation of the Si from the substrate. However, this layer closes at about half of the thickness (˜1.7 nm) for low-O conditions due to less oxidative conditions and less energetic particles arriving at the sample, which leads to less intermixing via silicate formation. In contrast, for high-O conditions, there is more ZrSiO4 and/or SiOx formation, giving more intermixing (˜3.4 nm). In vacuo X-ray photoelectron spectroscopy (XPS) measurements revealed similar stoichiometric ZrO2 layers deposited by both conditions and a higher interaction of the ZrO2 layer with the underlying a-Si for high-O conditions. In addition, oxygen diffusion through low-O ZrO2 films on a-Si has been investigated by ex situ angular-resolved XPS of samples annealed in atmospheric oxygen. For temperatures below 400 °C, no additional oxidation of the underlying a-Si was observed. This, together with the amorphous nature and smoothness of these samples, makes ZrO2 a good candidate as an oxidation protective layer on top of a-Si.

The Stellar Imager (SI) project: a deep space UV/Optical Interferometer (UVOI) to observe the Universe at 0.1 milli-arcsec angular resolution

NASA Astrophysics Data System (ADS)

Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

2009-04-01

The Stellar Imager (SI) is a space-based, UV/Optical Interferometer (UVOI) designed to enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and of the Universe in general. It will also probe via asteroseismology flows and structures in stellar interiors. SI’s science focuses on the role of magnetism in the Universe and will revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes, such as accretion, in the Universe. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI is a “Flagship and Landmark Discovery Mission” in the 2005 Heliophysics Roadmap and a potential implementation of the UVOI in the 2006 Science Program for NASA’s Astronomy and Physics Division. We present here the science goals of the SI Mission, a mission architecture that could meet those goals, and the technology development needed to enable this mission. Additional information on SI can be found at: http://hires.gsfc.nasa.gov/si/

siMacro: A Fast and Easy Data Processing Tool for Cell-Based Genomewide siRNA Screens.

PubMed

Singh, Nitin Kumar; Seo, Bo Yeun; Vidyasagar, Mathukumalli; White, Michael A; Kim, Hyun Seok

2013-03-01

Growing numbers of studies employ cell line-based systematic short interfering RNA (siRNA) screens to study gene functions and to identify drug targets. As multiple sources of variations that are unique to siRNA screens exist, there is a growing demand for a computational tool that generates normalized values and standardized scores. However, only a few tools have been available so far with limited usability. Here, we present siMacro, a fast and easy-to-use Microsoft Office Excel-based tool with a graphic user interface, designed to process single-condition or two-condition synthetic screen datasets. siMacro normalizes position and batch effects, censors outlier samples, and calculates Z-scores and robust Z-scores, with a spreadsheet output of >120,000 samples in under 1 minute.

siMacro: A Fast and Easy Data Processing Tool for Cell-Based Genomewide siRNA Screens

PubMed Central

Singh, Nitin Kumar; Seo, Bo Yeun; Vidyasagar, Mathukumalli; White, Michael A.

2013-01-01

Growing numbers of studies employ cell line-based systematic short interfering RNA (siRNA) screens to study gene functions and to identify drug targets. As multiple sources of variations that are unique to siRNA screens exist, there is a growing demand for a computational tool that generates normalized values and standardized scores. However, only a few tools have been available so far with limited usability. Here, we present siMacro, a fast and easy-to-use Microsoft Office Excel-based tool with a graphic user interface, designed to process single-condition or two-condition synthetic screen datasets. siMacro normalizes position and batch effects, censors outlier samples, and calculates Z-scores and robust Z-scores, with a spreadsheet output of >120,000 samples in under 1 minute. PMID:23613684

Improving Thermomechanical Properties of SiC/SiC Composites

NASA Technical Reports Server (NTRS)

DiCarlo, James A.; Bhatt, Ramakrishna T.

2006-01-01

Today, a major thrust toward improving the thermomechanical properties of engine components lies in the development of fiber-reinforced silicon carbide matrix composite materials, including SiC-fiber/SiC-matrix composites. These materials are lighter in weight and capable of withstanding higher temperatures, relative to state-of-the-art metallic alloys and oxide-matrix composites for which maximum use temperatures are in the vicinity of 1,100 C. In addition, the toughness or damage tolerance of the SiC-matrix composites is significantly greater than that of unreinforced silicon-based monolithic ceramics. For successful application in advanced engine systems, the SiC-matrix composites should be able to withstand component service stresses and temperatures for the desired component lifetimes. Inasmuch as the high-temperature structural lives of ceramic materials are typically limited by creep-induced growth of flaws, a key property required of such composite materials is high resistance to creep under conditions of use. Also, the thermal conductivity of the materials should be as high as possible so as to minimize component thermal gradients and thermal stresses. A state-of-the-art SiC-matrix composite is typically fabricated in a three-step process: (1) fabrication of a component-shaped architectural preform reinforced by thermally stable high-performance fibers, (2) chemical-vapor infiltration (CVI) of a fiber-coating material such as boron nitride (BN) into the preform, and (3) infiltration of an SiC-based matrix into the remaining porosity in the preform. Generally, the matrices of the highest-performing composites are fabricated by initial use of a CVI SiC matrix component that is typically more thermally stable and denser than matrix components formed by processes other than CVI. As such, the initial SiC matrix component made by CVI provides better environmental protection to the coated fibers embedded within it. Also, the denser CVI SiC imparts to the

Multiscale Engineered Si/SiO x Nanocomposite Electrodes for Lithium-Ion Batteries Using Layer-by-Layer Spray Deposition.

PubMed

Huang, Chun; Kim, Ayoung; Chung, Dong Jae; Park, Eunjun; Young, Neil P; Jurkschat, Kerstin; Kim, Hansu; Grant, Patrick S

2018-05-09

Si-based high-capacity materials have gained much attention as an alternative to graphite in Li-ion battery anodes. Although Si additions to graphite anodes are now commercialized, the fraction of Si that can be usefully exploited is restricted due to its poor cyclability arising from the large volume changes during charge/discharge. Si/SiO x nanocomposites have also shown promising behavior, such as better capacity retention than Si alone because the amorphous SiO x helps to accommodate the volume changes of the Si. Here, we demonstrate a new electrode architecture for further advancing the performance of Si/SiO x nanocomposite anodes using a scalable layer-by-layer atomization spray deposition technique. We show that particulate C interlayers between the current collector and the Si/SiO x layer and between the separator and the Si/SiO x layer improved electrical contact and reduced irreversible pulverization of the Si/SiO x significantly. Overall, the multiscale approach based on microstructuring at the electrode level combined with nanoengineering at the material level improved the capacity, rate capability, and cycling stability compared to that of an anode comprising a random mixture of the same materials.

SiGe nano-heteroepitaxy on Si and SiGe nano-pillars.

PubMed

Mastari, M; Charles, M; Bogumilowicz, Y; Thai, Q M; Pimenta-Barros, P; Argoud, M; Papon, A M; Gergaud, P; Landru, D; Kim, Y; Hartmann, J M

2018-07-06

In this paper, SiGe nano-heteroepitaxy on Si and SiGe nano-pillars was investigated in a 300 mm industrial reduced pressure-chemical vapour deposition tool. An integration scheme based on diblock copolymer patterning was used to fabricate nanometre-sized templates for the epitaxy of Si and SiGe nano-pillars. Results showed highly selective and uniform processes for the epitaxial growth of Si and SiGe nano-pillars. 200 nm thick SiGe layers were grown on Si and SiGe nano-pillars and characterised by atomic force microscopy, x-ray diffraction and transmission electron microscopy. Smooth SiGe surfaces and full strain relaxation were obtained in the 650 °C-700 °C range for 2D SiGe layers grown either on Si or SiGe nano-pillars.

Electron microscopy study of Ni induced crystallization in amorphous Si thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Radnóczi, G. Z.; Battistig, G.; Pécz, B., E-mail: pecz.bela@ttk.mta.hu

2015-02-17

The crystallization of amorphous silicon is studied by transmission electron microscopy. The effect of Ni on the crystallization is studied in a wide temperature range heating thinned samples in-situ inside the microscope. Two cases of limited Ni source and unlimited Ni source are studied and compared. NiSi{sub 2} phase started to form at a temperature as low as 250°C in the limited Ni source case. In-situ observation gives a clear view on the crystallization of silicon through small NiSi{sub 2} grain formation. The same phase is observed at the crystallization front in the unlimited Ni source case, where a secondmore » region is also observed with large grains of Ni{sub 3}Si{sub 2}. Low temperature experiments show, that long annealing of amorphous silicon at 410 °C already results in large crystallized Si regions due to the Ni induced crystallization.« less

Fluorescent carbon dots as an efficient siRNA nanocarrier for its interference therapy in gastric cancer cells.

PubMed

Wang, Qing; Zhang, Chunlei; Shen, Guangxia; Liu, Huiyang; Fu, Hualin; Cui, Daxiang

2014-12-30

Fluorescent carbon dots (Cdots) have attracted increasing attention due to their potential applications in sensing, catalysis, and biomedicine. Currently, intensive research has been concentrated on the synthesis and imaging-guided therapy of these benign photoluminescent materials. Meanwhile, Cdots have been explored as nonviral vector for nucleic acid or drug delivery by chemical modification on purpose. We have developed a microwave assisted one-step synthesis of Cdots with citric acid as carbon source and tryptophan (Trp) as both nitrogen source and passivation agent. The Cdots with uniform size show superior water solubility, excellent biocompatibility, and high quantum yield. Afterwards, the PEI (polyethylenimine)-adsorbed Cdots nanoparticles (Cdots@PEI) were applied to deliver Survivin siRNA into human gastric cancer cell line MGC-803. The results have confirmed the nanocarrier exhibited excellent biocompatibility and a significant increase in cellular delivery of siRNA, inducing efficient knockdown for Survivin protein to 6.1%. In addition, PEI@Cdots complexes mediated Survivin silencing, the arrested cell cycle progression in G1 phase as well as cell apoptosis was observed. The Cdots-based and PEI-adsorbed complexes both as imaging agents and siRNA nanocarriers have been developed for Survivin siRNA delivery. And the results indicate that Cdots-based nanocarriers could be utilized in a broad range of siRNA delivery systems for cancer therapy.

Preparation of siRNA encapsulated nanoliposomes suitable for siRNA delivery by simply discontinuous mixing.

PubMed

Mokhtarieh, Amir Abbas; Lee, Jieun; Kim, Semi; Lee, Myung Kyu

2018-06-01

Previously a scalable and extrusion-free method has been developed for efficient liposomal encapsulation of DNA by twice stepwise mixing of lipids in ethanol and DNA solution using T-shape mixing chamber. In this study, we prepared nanoliposomes encapsulating siRNA by simply discontinuous mixing of lipids in ethanol/ether/water mixture and acidic siRNA solution without use of special equipment. The simple mixing siRNA/liposomal particles (siRNA/SMLs) prepared using ethanol/ether/water (3:1:1) mixture showed 120.4 ± 20.2 nm particle size, 0.174 ± 0.033 polydispersity and 86.5 ± 2.76% siRNA encapsulation rate. In addition, the SMLs almost completely protected the encapsulated siRNA from RNase A digestion. Coupling of anti-human epidermal growth factor receptor (EGFR) Fab' to siRNA/SMLs enhanced EGFR-specific cell penetration of SMLs and induced siRNA dependent gene silencing. Unexpectedly, the Cy5.5-labeled Fab' showed almost no in vivo targeting to the xenografted A549 tumors in SCID-NOD mice. However, multiple injection of the unmodified siRNA/SMLs accumulated in the tumors and induced siRNA-dependent in vivo gene silencing. These results demonstrate that the siRNA/SMLs can be used as a siRNA delivery tool for gene therapy. Copyright © 2018 Elsevier B.V. All rights reserved.

Strain and Ge concentration determinations in SiGe/Si multiple quantum wells by transmission electron microscopy methods

NASA Astrophysics Data System (ADS)

Benedetti, A.; Norris, D. J.; Hetherington, C. J. D.; Cullis, A. G.; Robbins, D. J.; Wallis, D. J.

2003-04-01

SiGe/Si multiple quantum wells, nominally 4 nm thick, were grown by low pressure chemical vapor deposition and the Ge distribution within the wells was studied using a variety of transmission electron microscope-based techniques. Energy-dispersive x-ray spectroscopy and electron energy-loss imaging were used to directly measure the Ge compositional profile across the SiGe wells. In addition, the average Ge concentration was deduced indirectly from measurement of the strain-induced lattice displacements in high resolution images, obtained from the relative phase shift of the Si lattice planes on either side of a SiGe well. The results from both the direct and indirect measurement techniques were compared and found to be in good agreement with one another. The Ge profiles exhibited an asymmetric shape consistent with the occurrence of Ge segregation during growth. However, the amplitude of the asymmetry indicated that an additional factor, in particular gas dwell times within the reactor, also needed to be taken into account. Based upon this approach, a successful theoretical model of the growth process was derived.

Reduction in interface defect density in p-BaSi2/n-Si heterojunction solar cells by a modified pretreatment of the Si substrate

NASA Astrophysics Data System (ADS)

Yamashita, Yudai; Yachi, Suguru; Takabe, Ryota; Sato, Takuma; Emha Bayu, Miftahullatif; Toko, Kaoru; Suemasu, Takashi

2018-02-01

We have investigated defects that occurred at the interface of p-BaSi2/n-Si heterojunction solar cells that were fabricated by molecular beam epitaxy. X-ray diffraction measurements indicated that BaSi2 (a-axis-oriented) was subjected to in-plane compressive strain, which relaxed when the thickness of the p-BaSi2 layer exceeded 50 nm. Additionally, transmission electron microscopy revealed defects in the Si layer near steps that were present on the Si(111) substrate. Deep level transient spectroscopy revealed two different electron traps in the n-Si layer that were located at 0.33 eV (E1) and 0.19 eV (E2) below the conduction band edge. The densities of E1 and E2 levels in the region close to the heterointerface were approximately 1014 cm-3. The density of these electron traps decreased below the limits of detection following Si pretreatment to remove the oxide layers from the n-Si substrate, which involved heating the substrate to 800 °C for 30 min under ultrahigh vacuum while depositing a layer of Si (1 nm). The remaining traps in the n-Si layer were hole traps located at 0.65 eV (H1) and 0.38 eV (H2) above the valence band edge. Their densities were as low as 1010 cm-3. Following pretreatment, the current versus voltage characteristics of the p-BaSi2/n-Si solar cells under AM1.5 illumination were reproducible with conversion efficiencies beyond 5% when using a p-BaSi2 layer thickness of 100 nm. The origin of the H2 level is discussed.

Effect of hydrogen radical on decomposition of chlorosilane source gases

NASA Astrophysics Data System (ADS)

Sumiya, Masatomo; Akizuki, Tomohiro; Itaka, Kenji; Kubota, Makoto; Tsubouchi, Kenta; Ishigaki, Takamasa; Koinuma, Hideomi

2013-06-01

The effect of hydrogen radical on production of Si from chlorosilane sources has been studied. We used hydrogen radical generated from pulsed thermal plasma to decompose SiHCl3 and SiCl4. Hydrogen radical was effective for lowering the temperature to produce Si from SiHCl3. SiCl4 source, which was chemically stable and by-product in Siemens process, was decomposed effectively by hydrogen radical. The decomposition of SiCl4 was consistent with the thermo-dynamical calculation predicting that the use of hydrogen radical could drastically enhance the yield of Si production rather than case of H2 gas.

High throughput production of nanocomposite SiO x powders by plasma spray physical vapor deposition for negative electrode of lithium ion batteries.

PubMed

Homma, Keiichiro; Kambara, Makoto; Yoshida, Toyonobu

2014-04-01

Nanocomposite Si/SiO x powders were produced by plasma spray physical vapor deposition (PS-PVD) at a material throughput of 480 g h -1 . The powders are fundamentally an aggregate of primary ∼20 nm particles, which are composed of a crystalline Si core and SiO x shell structure. This is made possible by complete evaporation of raw SiO powders and subsequent rapid condensation of high temperature SiO x vapors, followed by disproportionation reaction of nucleated SiO x nanoparticles. When CH 4 was additionally introduced to the PS-PVD, the volume of the core Si increases while reducing potentially the SiO x shell thickness as a result of the enhanced SiO reduction, although an unfavorable SiC phase emerges when the C/Si molar ratio is greater than 1. As a result of the increased amount of Si active material and reduced source for irreversible capacity, half-cell batteries made of PS-PVD powders with C/Si = 0.25 have exhibited improved initial efficiency and maintenance of capacity as high as 1000 mAh g -1 after 100 cycles at the same time.

Effect of ZrB2 addition on the oxidation behavior of Si-SiC-ZrB2 composites exposed at 1500°C in air.

PubMed

D'Amico, Claudio; Bianchi, Giovanni; Padovano, Elisa; Biamino, Sara; Aversa, Alberta; Badini, Claudio; Ortona, Alberto

2018-01-01

Silicon carbide ceramics obtained by reactive infiltration of silicon (SRI) have many industrial applications especially involving severe and high temperature conditions. In this study, the oxidation behavior in air of Si-SiC-ZrB 2 systems at a high temperature (1500°C) for dwelling times of up to 48 hours was examined. The oxidation process was analyzed on the basis of elemental maps and X-ray diffraction patterns taken, respectively, on the core and on the surface of the specimens, together with weight gains and the average thicknesses of the resulting scale. Further, flexural strength at room temperature was examined as a function of different oxidation times. The main chemical reactions and phase transformations involved in the oxidation process are reported. Several oxides were detected on the surface: zirconia, silica, zircon and 3-zirconium monoxide. All of the samples showed a parabolic oxidation kinetics, suggesting that the controlling mechanism was the diffusion; however, even after 48 hours, the oxidation process was not finished - indeed, all of the samples continued to gain weight. The oxidation of Si-SiC-ZrB 2 material produced via SRI was slower compared with previously investigated ZrB 2 -SiC composites processed with a different techniques and tested in similar conditions. The oxidation mechanism was found to be consistent with the convection cells model.

X-ray photoelectron study of Si+ ion implanted polymers

NASA Astrophysics Data System (ADS)

Tsvetkova, T.; Balabanov, S.; Bischoff, L.; Krastev, V.; Stefanov, P.; Avramova, I.

2010-11-01

X-ray photoelectron spectroscopy was used to characterize different polymer materials implanted with low energy Si+ ions (E=30 keV, D= 1.1017 cm-2). Two kinds of polymers were studied - ultra-high-molecular-weight poly-ethylene (UHMWPE), and poly-methyl-methacrylate (PMMA). The non-implanted polymer materials show the expected variety of chemical bonds: carbon-carbon, carbon being three- and fourfold coordinated, and carbon-oxygen in the case of PMMA samples. The X-ray photoelectron and Raman spectra show that Si+ ion implantation leads to the introduction of additional disorder in the polymer material. The X-ray photoelectron spectra of the implanted polymers show that, in addition to already mentioned bonds, silicon creates new bonds with the host elements - Si-C and Si-O, together with additional Si dangling bonds as revealed by the valence band study of the implanted polymer materials.

A high performance pMOSFET with two-step recessed SiGe-S/D structure for 32 nm node and beyond

NASA Astrophysics Data System (ADS)

Yasutake, Nobuaki; Azuma, Atsushi; Ishida, Tatsuya; Ohuchi, Kazuya; Aoki, Nobutoshi; Kusunoki, Naoki; Mori, Shinji; Mizushima, Ichiro; Morooka, Tetsu; Kawanaka, Shigeru; Toyoshima, Yoshiaki

2007-11-01

A novel SiGe-S/D structure for high performance pMOSFET called two-step recessed SiGe-source/drain (S/D) is developed with careful optimization of recessed SiGe-S/D structure. With this method, hole mobility, short channel effect and S/D resistance in pMOSFET are improved compared with conventional recessed SiGe-S/D structure. To enhance device performance such as drain current drivability, SiGe region has to be closer to channel region. Then, conventional deep SiGe-S/D region with carefully optimized shallow SiGe SDE region showed additional device performance improvement without SCE degradation. As a result, high performance 24 nm gate length pMOSFET was demonstrated with drive current of 451 μA/μm at ∣ Vdd∣ of 0.9 V and Ioff of 100 nA/μm (552 μA/μm at ∣ Vdd∣ of 1.0 V). Furthermore, by combining with Vdd scaling, we indicate the extendability of two-step recessed SiGe-S/D structure down to 15 nm node generation.

Effects of annealing gas and drain doping concentration on electrical properties of Ge-source/Si-channel heterojunction tunneling FETs

NASA Astrophysics Data System (ADS)

Bae, Tae-Eon; Wakabayashi, Yuki; Nakane, Ryosho; Takenaka, Mitsuru; Takagi, Shinichi

2018-04-01

Improvement in the performance of Ge-source/Si-channel heterojunction tunneling FETs (TFETs) with high on-current/off-current (I on/I off) ratio and steep subthreshold swing (SS) is demonstrated. In this paper, we experimentally examine the effects of gas ambient [N2 and forming gas (4% H2/N2)] and a doping concentration in the drain regions on the electrical characteristics of Ge/Si heterojunction TFETs. The minimum SS (SSmin) of 70.9 mV/dec and the large I on/I off ratio of 1.4 × 107 are realized by postmetallization annealing in forming gas. Also, the steep SSmin and averaged SS (SSavr) values of 64.2 and 78.4 mV/dec, respectively, are obtained in low drain doping concentration. This improvement is attributable to the reduction in interface state density (D it) in the channel region and to the low leakage current in the drain region.

Green density variations in relation to colloidal packing in SiC/Si{sub 3}N{sub 4} composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crimp, M.J.; Oppermann, D.A.

1995-12-31

Composites of SiC/Si{sub 3}N{sub 4}, were produced using the processing conditions established in Stable Suspension{copyright}. This program utilizes Hogg, Healy and Furstenau`s modifications to DLVO theory to predict the stability conditions for composite suspensions. By altering the suspension pH, the conditions for SiC to SiC and Si{sub 3}N{sub 4} to Si{sub 3}N{sub 4} (homostability) attractions and the SiC to Si{sub 3}N{sub 4} (heterostability) attractions have been manipulated to obtain different green packing structures. The degree of homo- versus heterostability was controlled and the distribution of the Si{sub 3}N{sub 4} within the SiC determined. Additionally, this distribution was related to themore » green density of the composite. Results from density measurements versus the degree of homo- and heterocoagulation are presented along with SEM photomicrographs indicating the microstructural packing in the green body.« less

Amorphous sub-nanometre Tb-doped SiO(x)N(y)/SiO2 superlattices for optoelectronics.

PubMed

Ramírez, Joan Manel; Wojcik, Jacek; Berencén, Yonder; Ruiz-Caridad, Alícia; Estradé, Sònia; Peiró, Francesca; Mascher, Peter; Garrido, Blas

2015-02-27

Amorphous sub-nanometre Tb-doped SiOxNy/SiO2 superlattices were fabricated by means of alternating deposition of 0.7 nm thick Tb-doped SiOxNy layers and of 0.9 nm thick SiO2 barrier layers in an electron-cyclotron-resonance plasma enhanced chemical vapour deposition system with in situ Tb-doping capability. High resolution transmission electron microscopy images showed a well-preserved superlattice morphology after annealing at a high temperature of 1000 °C. In addition, transparent indium tin oxide (ITO) electrodes were deposited by electron beam evaporation using a shadow mask approach to allow for the optoelectronic characterization of superlattices. Tb(3+) luminescent spectral features were obtained using three different excitation sources: UV laser excitation (photoluminescence (PL)), under a bias voltage (electroluminescence (EL)) and under a highly energetic electron beam (cathodoluminescence (CL)). All techniques displayed Tb(3+) inner transitions belonging to (5)D4 levels except for the CL spectrum, in which (5)D3 transition levels were also observed. Two competing mechanisms were proposed to explain the spectral differences observed between PL (or EL) and CL excitation: the population rate of the (5)D3 state and the non-radiative relaxation rate of the (5)D3-(5)D4 transition due to a resonant OH-mode. Moreover, the large number of interfaces (trapping sites) that electrons have to get through was identified as the main reason for observing a bulk-limited charge transport mechanism governed by Poole-Frenkel conduction in the J-V characteristic. Finally, a linear EL-J dependence was measured, with independent spectral shape and an EL onset voltage as low as 6.7 V. These amorphous sub-nanometre superlattices are meant to provide low-cost solutions in different areas including sensing, photovoltaics or photonics.

Experimental Investigations on the effect of Additive on the Tensile Properties of Fiber Glass Fabric Lamina

NASA Astrophysics Data System (ADS)

Nava Sai Divya, A.; Raghu Kumar, B., Dr; Lakshmi Narayana, G., Dr

2017-09-01

The main objective of this work is to investigate the effect of additives on tensile behaviour of fiber glass fabric at lamina level to explore an alternative skin material for the outer body of aerospace applications and machines. This experimental work investigates the effect of silica concentration in epoxy resin lapox L-12 on the tensile properties of glass fabric lamina of 4H-satin weave having 3.6 mm thickness. The lamina was prepared by using hand lay-up method and tests were conducted on it. Various tensile properties values obtained from experimentation were compared for four glass fiber lamina composites fabricated by adding the silica powder to resin bath. The effect of variations in silica concentration (0% SiO2, 5% SiO2, 10% SiO2 and 15% SiO2) on the tensile properties of prepared material revealed that maximum stiffness was obtained at 15% and yield strength at 10% SiO2 concentration in glass fiber lamina. Increasing the silica concentration beyond 10% had led to deterioration in the material properties. The experimentation that was carried out on test specimen was reasonably successful as the effect of silica powder as an additive in glass fiber lamina enhanced the mechanical properties up to certain limit. The underpinning microscopic behaviour at the source of these observations will be investigated in a follow up work.

Dopant diffusion and segregation in semiconductor heterostructures: Part III, diffusion of Si into GaAs

NASA Astrophysics Data System (ADS)

Chen, C.-H.; Gösele, U. M.; Tan, T. Y.

We have mentioned previously that in the third part of the present series of papers, a variety of n-doping associated phenomena will be treated. Instead, we have decided that this paper, in which the subject treated is diffusion of Si into GaAs, shall be the third paper of the series. This choice is arrived at because this subject is a most relevent heterostructure problem, and also because of space and timing considerations. The main n-type dopant Si in GaAs is amphoteric which may be incorporated as shallow donor species SiGa+ and as shallow acceptor species SiAs-. The solubility of SiAs- is much lower than that of SiGa+ except at very high Si concentration levels. Hence, a severe electrical self-compensation occurs at very high Si concentrations. In this study we have modeled the Si distribution process in GaAs by assuming that the diffusing species is SiGa+ which will convert into SiAs- in accordance with their solubilities and that the point defect species governing the diffusion of SiGa+ are triply-negatively-charged Ga vacancies VGa3-. The outstanding features of the Si indiffusion profiles near the Si/GaAs interface have been quantitatively explained for the first time. Deposited on the GaAs crystal surface, the Si source material is a polycrystalline Si layer which may be undoped or n+-doped using As or P. Without the use of an As vapor phase in the ambient, the As- and P-doped source materials effectively render the GaAs crystals into an As-rich composition, which leads to a much more efficient Si indiffusion process than for the case of using undoped source materials which maintains the GaAs crystals in a relatively As-poor condition. The source material and the GaAs crystal together form a heterostructure with its junction influencing the electron distribution in the region, which, in turn, affects the Si indiffusion process prominently.

Submillimeter array observations of NGC 2264-C: molecular outflows and driving sources

NASA Astrophysics Data System (ADS)

Cunningham, Nichol; Lumsden, Stuart L.; Cyganowski, Claudia J.; Maud, Luke T.; Purcell, Cormac

2016-05-01

We present 1.3 mm Submillimeter Array (SMA) observations at ˜3 arcsec resolution towards the brightest section of the intermediate/massive star-forming cluster NGC 2264-C. The millimetre continuum emission reveals ten 1.3 mm continuum peaks, of which four are new detections. The observed frequency range includes the known molecular jet/outflow tracer SiO (5-4), thus providing the first high-resolution observations of SiO towards NGC 2264-C. We also detect molecular lines of 12 additional species towards this region, including CH3CN, CH3OH, SO, H2CO, DCN, HC3N, and 12CO. The SiO (5-4) emission reveals the presence of two collimated, high-velocity (up to 30 km s-1 with respect to the systemic velocity) bipolar outflows in NGC 2264-C. In addition, the outflows are traced by emission from 12CO, SO, H2CO, and CH3OH. We find an evolutionary spread between cores residing in the same parent cloud. The two unambiguous outflows are driven by the brightest mm continuum cores, which are IR-dark, molecular line weak, and likely the youngest cores in the region. Furthermore, towards the Red MSX Source AFGL 989-IRS1, the IR-bright and most evolved source in NGC 2264-C, we observe no molecular outflow emission. A molecular line rich ridge feature, with no obvious directly associated continuum source, lies on the edge of a low-density cavity and may be formed from a wind driven by AFGL 989-IRS1. In addition, 229 GHz class I maser emission is detected towards this feature.

Solution-derived sodalite made with Si- and Ge-ethoxide precursors for immobilizing electrorefiner salt

NASA Astrophysics Data System (ADS)

Riley, Brian J.; Lepry, William C.; Crum, Jarrod V.

2016-01-01

Chlorosodalite has the general form of Na8(AlSiO4)6Cl2 and this paper describes experiments conducted to synthesize sodalite with a solution-based approach to immobilize a simulated spent electrorefiner salt solution containing a mixture of alkali, alkaline earth, and lanthanide chlorides. The reactants used were the salt solution, NaAlO2, and either Si(OC2H5)4 or Ge(OC2H5)4. Additionally, seven different glass sintering aids (at loadings of 5 mass%) were evaluated as sintering aids for consolidating the as-made powders using a cold-press-and-sinter technique. This process of using alkoxide additives for the Group IV component can be used to produce large quantities of sodalite at near-room temperature as compared to a method where colloidal silica was used as the silica source. However, the small particle sizes inhibited densification during heat treatments.

Solution-derived sodalite made with Si- and Ge-ethoxide precursors for immobilizing electrorefiner salt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Riley, Brian J.; Lepry, William C.; Crum, Jarrod V.

Chlorosodalite has the general form of Na8(AlSiO4)6Cl2 and this paper describes experiments conducted to synthesize sodalite to immobilize a mixed chloride salt using solution-based techniques. Sodalites were made using different Group IV contributions from either Si(OC2H5)4 or Ge(OC2H5)4, NaAlO2, and a simulated spent electrorefiner salt solution containing a mixture of alkali, alkaline earth, and lanthanide chlorides. Additionally, 6 glass binders at low loadings of 5 mass% were evaluated as sintering aids for the consolidation process. The approach of using the organic Group IV additives can be used to produce large quantities of sodalite at room temperature and shows promise overmore » a method where colloidal silica is used as the silica source. However, the small particle sizes inhibited densification during pressure-less sintering.« less

Compared production behavior of borax and unborax premixed SiC reinforcement Al7Si-Mg-TiB alloys composites with semi-solid stir casting method

NASA Astrophysics Data System (ADS)

Haryono, M. B.; Sulardjaka, Nugroho, Sri

2016-04-01

The present study was aimed to investigate the effect of borax additive on physical and mechanical properties of Al7Si-Mg-TiB with the reinforcement of silicon carbide. In this case, the different weight percentage from the reinforcement of SiC (10, 15, and 20% wt), and the borax additive (ratio 1:4) were homogenously added into the matrix by employing the semi-solid stir casting method at the temperature of 590°C. Al7Si-Mg-TiB melted in an electric resistance furnace at 800°C for 25 minutes and the holding time of 5 minutes; SiC was stirred with borax inside the chamber and heated at the temperature of 250°C for 25 minutes. Then, it melted by lowing the temperature into 590°C. The SiC-borax mixture was added into the electric resistance furnace, and automatically stirred by the stirrer at a constant speed (500 rpm for 3 minutes) in the composite A17Si-Mg-TiB. It melted when heated at 750°C for 17minutes,then, casting was performed on the prepared mould. The characterizations of Al7Si-Mg-TiB-SiC/borax were porosity, hardness, and microstructure on the Al7Si-Mg-TiB-SiC/ borax. The porosity of AMC tended to increase along with the increaseof the wt% SiC (1.4%-3.6%); however, borax additive underwent a decrease in porosity (0.14%-1.3%). Further, hardness tended to improve along with the increase of wt% SiC. The unboraxmixture had 79,6 HRB up to 94 HRB. Whereas, the borax additive mixture had 105,8 HRB up to 121 HRB.

Additive Partial Least Squares for efficient modelling of independent variance sources demonstrated on practical case studies.

PubMed

Luoma, Pekka; Natschläger, Thomas; Malli, Birgit; Pawliczek, Marcin; Brandstetter, Markus

2018-05-12

A model recalibration method based on additive Partial Least Squares (PLS) regression is generalized for multi-adjustment scenarios of independent variance sources (referred to as additive PLS - aPLS). aPLS allows for effortless model readjustment under changing measurement conditions and the combination of independent variance sources with the initial model by means of additive modelling. We demonstrate these distinguishing features on two NIR spectroscopic case-studies. In case study 1 aPLS was used as a readjustment method for an emerging offset. The achieved RMS error of prediction (1.91 a.u.) was of similar level as before the offset occurred (2.11 a.u.). In case-study 2 a calibration combining different variance sources was conducted. The achieved performance was of sufficient level with an absolute error being better than 0.8% of the mean concentration, therefore being able to compensate negative effects of two independent variance sources. The presented results show the applicability of the aPLS approach. The main advantages of the method are that the original model stays unadjusted and that the modelling is conducted on concrete changes in the spectra thus supporting efficient (in most cases straightforward) modelling. Additionally, the method is put into context of existing machine learning algorithms. Copyright © 2018 Elsevier B.V. All rights reserved.

Abundance of SiC2 in carbon star envelopes

NASA Astrophysics Data System (ADS)

Massalkhi, S.; Agúndez, M.; Cernicharo, J.; Velilla Prieto, L.; Goicoechea, J. R.; Quintana-Lacaci, G.; Fonfría, J. P.; Alcolea, J.; Bujarrabal, V.

2018-03-01

Context. Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich asymptotic giant branch (AGB) stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si-C bond detected in C-rich AGB stars are SiC2, SiC, and Si2C. To date, the ring molecule SiC2 has been observed in a handful of evolved stars, while SiC and Si2C have only been detected in the C-star envelope IRC +10216. Aim. We aim to study how widespread and abundant SiC2, SiC, and Si2C are in envelopes around C-rich AGB stars, and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars. Methods: We carried out sensitive observations with the IRAM 30 m telescope of a sample of 25 C-rich AGB stars to search for emission lines of SiC2, SiC, and Si2C in the λ 2 mm band. We performed non-LTE excitation and radiative transfer calculations based on the LVG method to model the observed lines of SiC2 and to derive SiC2 fractional abundances in the observed envelopes. Results: We detect SiC2 in most of the sources, SiC in about half of them, and do not detect Si2C in any source except IRC +10216. Most of these detections are reported for the first time in this work. We find a positive correlation between the SiC and SiC2 line emission, which suggests that both species are chemically linked; the SiC radical is probably the photodissociation product of SiC2 in the external layer of the envelope. We find a clear trend where the denser the envelope, the less abundant SiC2 is. The observed trend is interpreted as evidence of efficient incorporation of SiC2 onto dust grains, a process that is favored at high densities owing to the higher rate at which collisions between particles take place. Conclusions: The observed behavior of a decline in the SiC2 abundance with increasing density strongly suggests that SiC2 is an

Synthesis and characterization of AlTiSiN/CrSiN multilayer coatings by cathodic arc ion-plating

NASA Astrophysics Data System (ADS)

Yang, B.; Tian, C. X.; Wan, Q.; Yan, S. J.; Liu, H. D.; Wang, R. Y.; Li, Z. G.; Chen, Y. M.; Fu, D. J.

2014-09-01

AlTiSiN/CrSiN multilayer coatings were deposited on Si (1 0 0) and cemented carbide substrates using Cr, AlTi cathodes and SiH4 gases by cathodic arc ion plating system. The influences of SiH4 gases flowrate on the structural and mechanical properties of the coatings were investigated, systematically. AlTiSiN/CrSiN coatings exhibit a B1 NaCl-type nano-multilayered structure in which the CrSiN nano-layers alternate with AlTiSiN nano-layers with multiple orientations of crystal planes indicated by XRD patterns and TEM. Si contents of the coatings increase with increasing SiH4 flowrate. The hardness of the coatings increases to the maximum value of 3500 Hv0.05 with increasing SiH4 flowrate from 20 to 40 sccm and then decreases with further addition of SiH4 gases. A higher adhesive force of 73 N is obtained at the flowrate of 48 sccm. The coatings exhibit different tribological performance when the mating materials were varied from Si3N4 to cemented carbide balls and the variation of friction coefficients of the coatings against Si3N4 influenced by SiH4 flowrate are not obvious as against cemented carbide balls.

Effect of an external magnetic field on the mass attenuation coefficients of p-Si and n-Si

NASA Astrophysics Data System (ADS)

Yılmaz, D.; Önder, P.

2018-05-01

In this study, the mass attenuation coefficients of p-Si and n-Si semiconductor samples have been determined in an external magnetic field. The semiconductor samples were located to the external magnetic field of intensities 0.2 T, 0.4 T, 0.6 T and 0.8 T. The samples were bombarded by 59.5 keV, 80.1 keV, 121.8 keV and 244.7 keV gamma-rays emitted from Am241, Ba133 and Eu152 radioactive sources. The transmitted photons were detected by a CdTe detector. It was observed that the mass attenuation coefficients of p-Si and n-Si semiconductor samples decrease with increasing gamma-ray energy. Also, the mass attenuation coefficients of the samples increase with applying magnetic field intensity.

Consolidation of silicon nitride without additives

NASA Technical Reports Server (NTRS)

Sikora, P. F.; Yeh, H. C.

1977-01-01

The feasibility of producing a sound, dense Si3N4 body without additives was explored, using conventional gas hot isostatic pressing techniques and an uncommon hydraulic hot isostatic pressing technique. These two techniques produce much higher pressure 275-413 MN/m sq (40,000 - 60,000 psi) than hot-pressing techniques. Evaluation was based on density measurement, microscopic examination, both optical and electron, and X-ray diffraction analysis. The results are summarized as follows: (1) Si3N4 can be densified to high density, greater than 95% of theoretical, without additions. (2) The higher density Si3N4 specimens appear to be associated with a greater amount of alpha to beta transformation. (3) Under high pressure, the alpha to beta transformation can occur at a temperature as low as 1150 C. (4) Grain deformation and subsequent recrystallization and grain refinement result from hot isostatic pressing of Si3N4.

Interfacial mixing in as-deposited Si/Ni/Si layers analyzed by x-ray and polarized neutron reflectometry

NASA Astrophysics Data System (ADS)

Bhattacharya, Debarati; Basu, Saibal; Singh, Surendra; Roy, Sumalay; Dev, Bhupendra Nath

2012-12-01

Interdiffusion occurring across the interfaces in a Si/Ni/Si layered system during deposition at room temperature was probed using x-ray reflectivity (XRR) and polarized neutron reflectivity (PNR). Exploiting the complementarity of these techniques, both structural and magnetic characterization with nanometer depth resolution could be achieved. Suitable model fitting of the reflectivity profiles identified the formation of Ni-Si mixed alloy layers at the Si/Ni and Ni/Si interfaces. The physical parameters of the layered structure, including quantitative assessment of the stoichiometry of interfacial alloys, were obtained from the analyses of XRR and PNR patterns. In addition, PNR provided magnetic moment density profile as a function of depth in the stratified medium.

siRNA Delivery to the Glomerular Mesangium Using Polycationic Cyclodextrin Nanoparticles Containing siRNA

PubMed Central

Gale, Aaron; Wu, Peiwen; Ma, Rong; Davis, Mark E.

2015-01-01

There is an urgent need for new therapies that can halt or reverse the course of chronic kidney disease with minimal side-effect burden on the patient. Small interfering RNA (siRNA) nanoparticles are new therapeutic entities in clinical development that could be useful for chronic kidney disease treatment because they combine the tissue-specific targeting properties of nanoparticles with the gene-specific silencing effects of siRNA. Recent reports have emerged demonstrating that the kidney, specifically the glomerulus, is a readily accessible site for nanoparticle targeting. Here, we explore the hypothesis that intravenously administered polycationic cyclodextrin nanoparticles containing siRNA (siRNA/CDP-NPs) can be used for delivery of siRNA to the glomerular mesangium. We demonstrate that siRNA/CDP-NPs localize to the glomerular mesangium with limited deposition in other areas of the kidney after intravenous injection. Additionally, we report that both mouse and human mesangial cells rapidly internalize siRNA/CDP-NPs in vitro and that nanoparticle uptake can be enhanced by attaching the targeting ligands mannose or transferrin to the nanoparticle surface. Lastly, we show knockdown of mesangial enhanced green fluorescent protein expression in a reporter mouse strain following iv treatment with siRNA/CDP-NPs. Altogether, these data demonstrate the feasibility of mesangial targeting using intravenously administered siRNA/CDP-NPs. PMID:25734248

Antioxidant migration resistance of SiOx layer in SiOx/PLA coated film.

PubMed

Huang, Chongxing; Zhao, Yuan; Su, Hongxia; Bei, Ronghua

2018-02-01

As novel materials for food contact packaging, inorganic silicon oxide (SiO x ) films are high barrier property materials that have been developed rapidly and have attracted the attention of many manufacturers. For the safe use of SiO x films for food packaging it is vital to study the interaction between SiO x layers and food contaminants, as well as the function of a SiO x barrier layer in antioxidant migration resistance. In this study, we deposited a SiO x layer on polylactic acid (PLA)-based films to prepare SiO x /PLA coated films by plasma-enhanced chemical vapour deposition. Additionally, we compared PLA-based films and SiO x /PLA coated films in terms of the migration of different antioxidants (e.g. t-butylhydroquinone [TBHQ], butylated hydroxyanisole [BHA], and butylated hydroxytoluene [BHT]) via specific migration experiments and then investigated the effects of a SiO x layer on antioxidant migration under different conditions. The results indicate that antioxidant migration from SiO x /PLA coated films is similar to that for PLA-based films: with increase of temperature, decrease of food simulant polarity, and increase of single-sided contact time, the antioxidant migration rate and amount in SiO x /PLA coated films increase. The SiO x barrier layer significantly reduced the amount of migration of antioxidants with small and similar molecular weights and similar physical and chemical properties, while the degree of migration blocking was not significantly different among the studied antioxidants. However, the migration was affected by temperature and food simulant. Depending on the food simulants considered, the migration amount in SiO x /PLA coated films was reduced compared with that in PLA-based films by 42-46%, 44-47%, and 44-46% for TBHQ, BHA, and BHT, respectively.

Controlled growth of 3C-SiC and 6H-SiC films on low-tilt-angle vicinal (0001) 6H-SiC wafers

NASA Technical Reports Server (NTRS)

Powell, J. A.; Petit, J. B.; Edgar, J. H.; Jenkins, I. G.; Matus, L. G.

1991-01-01

It has been found that, with proper pregrowth surface treatment, 6H-SiC single-crystal films can be grown by chemical vapor deposition (CVD) at 1450 C on vicinal (0001) 6H-SiC with tilt angles as small as 0.1 deg. Previously, tilt angles of greater than 1.5 deg were required to achieve 6H on 6H at this growth temperature. In addition, 3C-SiC could be induced to grow within selected regions on the 6H substrate. the 3C regions contained few (or zero) double-positioning boundaries and a low density of stacking faults. A new growth model is proposed to explain the control of SiC polytype in this epitaxial film growth process.

Rear-Sided Passivation by SiNx:H Dielectric Layer for Improved Si/PEDOT:PSS Hybrid Heterojunction Solar Cells.

PubMed

Sun, Yiling; Gao, Pingqi; He, Jian; Zhou, Suqiong; Ying, Zhiqin; Yang, Xi; Xiang, Yong; Ye, Jichun

2016-12-01

Silicon/organic hybrid solar cells have recently attracted great attention because they combine the advantages of silicon (Si) and the organic cells. In this study, we added a patterned passivation layer of silicon nitride (SiNx:H) onto the rear surface of the Si substrate in a Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PSS) hybrid solar cell, enabling an improvement of 0.6 % in the power conversion efficiency (PCE). The addition of the SiNx:H layer boosted the open circuit voltage (V oc) from 0.523 to 0.557 V, suggesting the well-passivation property of the patterned SiNx:H thin layer that was created by plasma-enhanced chemical vapor deposition and lithography processes. The passivation properties that stemmed from front PSS, rear-SiNx:H, front PSS/rear-SiNx:H, etc. are thoroughly investigated, in consideration of the process-related variations.

Epitaxial CoSi2 on MOS devices

DOEpatents

Lim, Chong Wee; Shin, Chan Soo; Petrov, Ivan Georgiev; Greene, Joseph E.

2005-01-25

An Si.sub.x N.sub.y or SiO.sub.x N.sub.y liner is formed on a MOS device. Cobalt is then deposited and reacts to form an epitaxial CoSi.sub.2 layer underneath the liner. The CoSi.sub.2 layer may be formed through a solid phase epitaxy or reactive deposition epitaxy salicide process. In addition to high quality epitaxial CoSi.sub.2 layers, the liner formed during the invention can protect device portions during etching processes used to form device contacts. The liner can act as an etch stop layer to prevent excessive removal of the shallow trench isolation, and protect against excessive loss of the CoSi.sub.2 layer.

Fabrication and Analysis of the Wear Properties of Hot-Pressed Al-Si/SiCp + Al-Si-Cu-Mg Metal Matrix Composite

NASA Astrophysics Data System (ADS)

Bang, Jeongil; Oak, Jeong-Jung; Park, Yong Ho

2016-01-01

The aim of this study was to characterize microstructures and mechanical properties of aluminum metal matrix composites (MMC's) prepared by powder metallurgy method. Consolidation of mixed powder with gas atomized Al-Si/SiCp powder and Al-14Si-2.5Cu-0.5Mg powder by hot pressing was classified according to sintering temperature and sintering time. Sintering condition was optimized using tensile properties of sintered specimens. Ultimate tensile strength of the optimized sintered specimen was 228 MPa with an elongation of 5.3% in longitudinal direction. In addition, wear properties and behaviors of the sintered aluminum-based MMC's were analyzed in accordance with vertical load and linear speed. As the linear speed and vertical load of the wear increased, change of the wear behavior occurred in order of oxidation of Al-Si matrix, formation of C-rich layer, Fe-alloying to matrix, and melting of the specimen

Landscape cultivation alters δ30Si signature in terrestrial ecosystems.

NASA Astrophysics Data System (ADS)

Vandevenne, F. I.; Delvaux, C.; Huyghes, H.; Ronchi, B.; Govers, G.; Barão, A. L.; Clymans, W.; Meire, P.; André, L.; Struyf, E.

2014-12-01

Despite increasing recognition of the importance of biological Si cycling in controlling dissolved Si (DSi) in soil and stream water, effects of human cultivation on the Si cycle remain poorly understood. Sensitive tracer techniques to identify and quantify Si in the soil-plant-water system could be highly relevant in addressing these uncertainties. Stable Si isotopes are promising tools to define Si sources and sinks along the ecosystem flow path, as intense fractionation occurs during chemical weathering and uptake of dissolved Si in plants. Yet they remain underexploited in the end product of the soil-plant system: the soil water. Here, stable Si isotope ratios (δ30Si) of dissolved Si in soil water were measured along a land use gradient (continuous forest, continuous pasture, young cropland and continuous cropland) with similar parent material (loess) and homogenous bulk mineralogical and climatological properties (Belgium). Soil water δ30Si signatures are clearly separated along the gradient, with highest average signatures in continuous cropland (+1.61‰), intermediate in pasture (+1.05‰) and young cropland (+0.89 ‰) and lowest in forest soil water (+0.62‰). Our data do not allow distinguishing biological from pedogenic/lithogenic processes, but point to a strong interaction of both. We expect that increasing export of light isotopes in disturbed land uses (i.e. through agricultural harvest), and higher recycling of 28Si and elevated weathering intensity (including clay dissolution) in forest systems will largely determine soil water δ30Si signatures of our systems. Our results imply that soil water δ30Si signature is biased through land management before it reaches rivers and coastal zones, where other fractionation processes take over (e.g. diatom uptake and reverse weathering in floodplains). In particular, a direct role of agriculture systems in lowering export Si fluxes towards rivers and coastal systems has been shown. Stable Si isotopes have

Landscape cultivation alters δ30Si signature in terrestrial ecosystems

NASA Astrophysics Data System (ADS)

Vandevenne, Floor; Delvaux, Claire; Hughes, Harold; Ronchi, Benedicta; Clymans, Wim; Barao, Ana Lucia; Govers, Gerard; Cornelis, Jean Thomas; André, Luc; Struyf, Eric

2015-04-01

Despite increasing recognition of the importance of biological Si cycling in controlling dissolved Si (DSi) in soil and stream water, effects of human cultivation on the Si cycle remain poorly understood. Sensitive tracer techniques to identify and quantify Si in the soil-plant-water system could be highly relevant in addressing these uncertainties. Stable Si isotopes are promising tools to define Si sources and sinks along the ecosystem flow path, as intense fractionation occurs during chemical weathering and uptake of dissolved Si in plants. Yet they remain underexploited in the end product of the soil-plant system: the soil water. Here, stable Si isotope ratios (δ30Si) of dissolved Si in soil water were measured along a land use gradient (continuous forest, continuous pasture, young cropland and continuous cropland) with similar parent material (loess) and homogenous bulk mineralogical and climatological (Belgium). Soil water δ30Si signatures are clearly separated along the gradient, with highest average signatures in continuous cropland (+1.61%), intermediate in pasture (+1.05%) and young cropland (+0.89%) and lowest in forest soil water (+0.62%). Our data do not allow distinguishing biological from pedogenic/lithogenic processes, but point to a strong interaction of both. We expect that increasing export of light isotopes in disturbed land uses (i.e. through agricultural harvest), and higher recycling of 28Si and elevated weathering intensity (including clay dissolution) in forest systems will largely determine soil water δ30Si signatures of our systems. Our results imply that soil water δ30Si signature is biased through land management before it reaches rivers and coastal zones, where other fractionation processes take over (e.g. diatom uptake and reverse weathering in floodplains). In particular, a direct role of agriculture systems in lowering export Si fluxes towards rivers and coastal systems has been shown. Stable Si isotopes have a large potential

Glycerol as an additional carbon source for bacterial cellulose synthesis

NASA Astrophysics Data System (ADS)

Agustin, Y. E.; Padmawijaya, K. S.; Rixwari, H. F.; Yuniharto, V. A. S.

2018-03-01

Bacterial cellulose, the fermentation result of Acetobacter xylinus can be produced when glycerol was used as an additional carbon source. In this research, bacterial cellulose produced in two different fermentation medium, Hestrin and Scharmm (HS) medium and HS medium with additional MgSO4. Concentration of glycerol that used in this research were 0%; 5%; 10%; and 15% (v/v). The optimum conditions of bacterial cellulose production on each experiment variations determined by characterization of the mechanical properties, including thickness, tensile strength and elongation. Fourier Transform Infra Red Spectroscopy (FTIR) revealed the characterization of bacterial cellulose. Results showed that the growth rate of bacterial cellulose in HS-MgSO4-glycerol medium was faster than in HS-glycerol medium. Increasing concentrations of glycerol will lower the value of tensile strength and elongation. Elongation test showed that the elongation bacterial cellulose (BC) with the addition of 4.95% (v/v) glycerol in the HS-MgSO4 medium is the highest elongation value. The optimum bacterial cellulose production was achieved when 4.95% (v/v) of glycerol added into HS-MgSO4 medium with stress at break of 116.885 MPa and 4.214% elongation.

Real time dynamics of Si magic clusters mediating phase transformation: Si(111)-(1 × 1) to (7 × 7) reconstruction revisited

NASA Astrophysics Data System (ADS)

Ong, Wei Jie; Tok, Eng Soon

2012-07-01

Using Scanning Tunneling Microscope (STM), we show that the surface undergoes phase transformation from disordered "1 × 1" to (7 × 7) reconstruction which is mediated by the formation of Si magic clusters. Mono-disperse Si magic clusters of size ~ 13.5 ± 0.5 Å can be formed by heating the Si(111) surface to 1200 °C and quenching it to room temperature at cooling rates of at least 100 °C/min. The structure consists of 3 tetra-clusters of size ~ 4.5 Ǻ similar to the Si magic clusters that were formed from Si adatoms deposited by Si solid source on Si(111)-(7 × 7) [1]. Using real time STM scanning to probe the surface at ~ 400 °C, we show that Si magic clusters pop up from the (1 × 1) surface and form spontaneously during the phase transformation. This is attributed to the difference in atomic density between "disordered 1 × 1" and (7 × 7) surface structures which lead to the release of excess Si atoms onto the surface as magic clusters.

Space electric field concentrated effect for Zr:SiO2 RRAM devices using porous SiO2 buffer layer

PubMed Central

2013-01-01

To improve the operation current lowing of the Zr:SiO2 RRAM devices, a space electric field concentrated effect established by the porous SiO2 buffer layer was investigated and found in this study. The resistive switching properties of the low-resistance state (LRS) and high-resistance state (HRS) in resistive random access memory (RRAM) devices for the single-layer Zr:SiO2 and bilayer Zr:SiO2/porous SiO2 thin films were analyzed and discussed. In addition, the original space charge limited current (SCLC) conduction mechanism in LRS and HRS of the RRAM devices using bilayer Zr:SiO2/porous SiO2 thin films was found. Finally, a space electric field concentrated effect in the bilayer Zr:SiO2/porous SiO2 RRAM devices was also explained and verified by the COMSOL Multiphysics simulation model. PMID:24330524

Cell-penetrating peptide-siRNA conjugate loaded YSA-modified nanobubbles for ultrasound triggered siRNA delivery.

PubMed

Xie, Xiangyang; Yang, Yanfang; Lin, Wen; Liu, Hui; Liu, Hong; Yang, Yang; Chen, Ying; Fu, Xudong; Deng, Jianping

2015-12-01

Due to the absence of effective in vivo delivery systems, the employment of small interference RNA (siRNA) in the clinic has been hindered. In this paper, a new siRNA targeting system for EphA2-positive tumors was developed, based on ultrasound-sensitive nanobubbles (NBs) and cell-permeable peptides (CPPs). Here, a CPP-siRNA conjugate (CPP-siRNA) was entrapped in an ephrin mimetic peptide (YSA peptide)-modified NB (CPP-siRNA/YSA-NB) and the penetration of the CPP-siRNA was temporally masked; local ultrasound stimulation triggered the release of CPP-siRNA from the NBs and activated its penetration. Subsequent research demonstrated that the CPP-siRNA/YSA-NBs had particle sizes of approximately 200 nm and a siRNA entrapment efficiency of more than 85%. The in vitro release results showed that over 90% of the encapsulated CPP-siRNA released from the NBs in the presence of ultrasound, while less than 1.5% of that (30 min) released without ultrasound. Cell experiments showed a the higher CPP-siRNA cellular uptake of CPP-siRNA/YSA-NB among the various formulations in human breast adenocarcinoma cells (MCF-7, EphA2 positive cells). Additionally, after systemic administration in mice, CPP-siRNA/YSA-NB accumulated in the tumor, augmented c-Myc silencing and delayed tumor progression. In conclusion, the application of CPP-siRNA/YSA-NB with ultrasound may provide a strategy for the selective and efficient delivery of siRNA. Copyright © 2015 Elsevier B.V. All rights reserved.

Engineering of band gap states of amorphous SiZnSnO semiconductor as a function of Si doping concentration.

PubMed

Choi, Jun Young; Heo, Keun; Cho, Kyung-Sang; Hwang, Sung Woo; Kim, Sangsig; Lee, Sang Yeol

2016-11-04

We investigated the band gap of SiZnSnO (SZTO) with different Si contents. Band gap engineering of SZTO is explained by the evolution of the electronic structure, such as changes in the band edge states and band gap. Using ultraviolet photoelectron spectroscopy (UPS), it was verified that Si atoms can modify the band gap of SZTO thin films. Carrier generation originating from oxygen vacancies can modify the band-gap states of oxide films with the addition of Si. Since it is not easy to directly derive changes in the band gap states of amorphous oxide semiconductors, no reports of the relationship between the Fermi energy level of oxide semiconductor and the device stability of oxide thin film transistors (TFTs) have been presented. The addition of Si can reduce the total density of trap states and change the band-gap properties. When 0.5 wt% Si was used to fabricate SZTO TFTs, they showed superior stability under negative bias temperature stress. We derived the band gap and Fermi energy level directly using data from UPS, Kelvin probe, and high-resolution electron energy loss spectroscopy analyses.

Engineering of band gap states of amorphous SiZnSnO semiconductor as a function of Si doping concentration

PubMed Central

Choi, Jun Young; Heo, Keun; Cho, Kyung-Sang; Hwang, Sung Woo; Kim, Sangsig; Lee, Sang Yeol

2016-01-01

We investigated the band gap of SiZnSnO (SZTO) with different Si contents. Band gap engineering of SZTO is explained by the evolution of the electronic structure, such as changes in the band edge states and band gap. Using ultraviolet photoelectron spectroscopy (UPS), it was verified that Si atoms can modify the band gap of SZTO thin films. Carrier generation originating from oxygen vacancies can modify the band-gap states of oxide films with the addition of Si. Since it is not easy to directly derive changes in the band gap states of amorphous oxide semiconductors, no reports of the relationship between the Fermi energy level of oxide semiconductor and the device stability of oxide thin film transistors (TFTs) have been presented. The addition of Si can reduce the total density of trap states and change the band-gap properties. When 0.5 wt% Si was used to fabricate SZTO TFTs, they showed superior stability under negative bias temperature stress. We derived the band gap and Fermi energy level directly using data from UPS, Kelvin probe, and high-resolution electron energy loss spectroscopy analyses. PMID:27812035

BaSi2 formation mechanism in thermally evaporated films and its application to reducing oxygen impurity concentration

NASA Astrophysics Data System (ADS)

Hara, Kosuke O.; Yamamoto, Chiaya; Yamanaka, Junji; Arimoto, Keisuke; Nakagawa, Kiyokazu; Usami, Noritaka

2018-04-01

Thermal evaporation is a simple and rapid method to fabricate semiconducting BaSi2 films. In this study, to elucidate the BaSi2 formation mechanism, the microstructure of a BaSi2 epitaxial film fabricated by thermal evaporation has been investigated by transmission electron microscopy. The BaSi2 film is found to consist of three layers with different microstructural characteristics, which is well explained by assuming two stages of film deposition. In the first stage, BaSi2 forms through the diffusion of Ba atoms from the deposited Ba-rich film to the Si substrate while in the second stage, the mutual diffusion of Ba and Si atoms in the film leads to BaSi2 formation. On the basis of the BaSi2 formation mechanism, two issues are addressed. One is the as-yet unclarified reason for epitaxial growth. It is found important to quickly form BaSi2 in the first stage for the epitaxial growth of upper layers. The other issue is the high oxygen concentration in BaSi2 films around the BaSi2-Si interface. Two routes of oxygen incorporation, i.e., oxidation of the Si substrate surface and initially deposited Ba-rich layer by the residual gas, are identified. On the basis of this knowledge, oxygen concentration is decreased by reducing the holding time of the substrate at high temperatures and by premelting of the source. In addition, X-ray diffraction results show that the decrease in oxygen concentration can lead to an increased proportion of a-axis-oriented grains.

Si-Based Germanium Tin Semiconductor Lasers for Optoelectronic Applications

NASA Astrophysics Data System (ADS)

Al-Kabi, Sattar H. Sweilim

Silicon-based materials and optoelectronic devices are of great interest as they could be monolithically integrated in the current Si complementary metal-oxide-semiconductor (CMOS) processes. The integration of optoelectronic components on the CMOS platform has long been limited due to the unavailability of Si-based laser sources. A Si-based monolithic laser is highly desirable for full integration of Si photonics chip. In this work, Si-based germanium-tin (GeSn) lasers have been demonstrated as direct bandgap group-IV laser sources. This opens a completely new avenue from the traditional III-V integration approach. In this work, the material and optical properties of GeSn alloys were comprehensively studied. The GeSn films were grown on Ge-buffered Si substrates in a reduced pressure chemical vapor deposition system with low-cost SnCl4 and GeH4 precursors. A systematic study was done for thin GeSn films (thickness 400 nm) with Sn composition 5 to 17.5%. The room temperature photoluminescence (PL) spectra were measured that showed a gradual shift of emission peaks towards longer wavelength as Sn composition increases. Strong PL intensity and low defect density indicated high material quality. Moreover, the PL study of n-doped samples showed bandgap narrowing compared to the unintentionally p-doped (boron) thin films with similar Sn compositions. Finally, optically pumped GeSn lasers on Si with broad wavelength coverage from 2 to 3 mum were demonstrated using high-quality GeSn films with Sn compositions up to 17.5%. The achieved maximum Sn composition of 17.5% broke the acknowledged Sn incorporation limit using similar deposition chemistry. The highest lasing temperature was measured at 180 K with an active layer thickness as thin as 270 nm. The unprecedented lasing performance is due to the achievement of high material quality and a robust fabrication process. The results reported in this work show a major advancement towards Si-based electrically pumped mid

Investigation of interface property in Al/SiO2/ n-SiC structure with thin gate oxide by illumination

NASA Astrophysics Data System (ADS)

Chang, P. K.; Hwu, J. G.

2017-04-01

The reverse tunneling current of Al/SiO2/ n-SiC structure employing thin gate oxide is introduced to examine the interface property by illumination. The gate current at negative bias decreases under blue LED illumination, yet increases under UV lamp illumination. Light-induced electrons captured by interface states may be emitted after the light sources are off, leading to the recovery of gate currents. Based on transient characteristics of gate current, the extracted trap level is close to the light energy for blue LED, indicating that electron capture induced by lighting may result in the reduction of gate current. Furthermore, bidirectional C- V measurements exhibit a positive voltage shift caused by electron trapping under blue LED illumination, while a negative voltage shift is observed under UV lamp illumination. Distinct trapping and detrapping behaviors can be observed from variations in I- V and C- V curves utilizing different light sources for 4H-SiC MOS capacitors with thin insulators.

Improved nucleic acid descriptors for siRNA efficacy prediction.

PubMed

Sciabola, Simone; Cao, Qing; Orozco, Modesto; Faustino, Ignacio; Stanton, Robert V

2013-02-01

Although considerable progress has been made recently in understanding how gene silencing is mediated by the RNAi pathway, the rational design of effective sequences is still a challenging task. In this article, we demonstrate that including three-dimensional descriptors improved the discrimination between active and inactive small interfering RNAs (siRNAs) in a statistical model. Five descriptor types were used: (i) nucleotide position along the siRNA sequence, (ii) nucleotide composition in terms of presence/absence of specific combinations of di- and trinucleotides, (iii) nucleotide interactions by means of a modified auto- and cross-covariance function, (iv) nucleotide thermodynamic stability derived by the nearest neighbor model representation and (v) nucleic acid structure flexibility. The duplex flexibility descriptors are derived from extended molecular dynamics simulations, which are able to describe the sequence-dependent elastic properties of RNA duplexes, even for non-standard oligonucleotides. The matrix of descriptors was analysed using three statistical packages in R (partial least squares, random forest, and support vector machine), and the most predictive model was implemented in a modeling tool we have made publicly available through SourceForge. Our implementation of new RNA descriptors coupled with appropriate statistical algorithms resulted in improved model performance for the selection of siRNA candidates when compared with publicly available siRNA prediction tools and previously published test sets. Additional validation studies based on in-house RNA interference projects confirmed the robustness of the scoring procedure in prospective studies.

Effects of the addition of different nitrogen sources in the tequila fermentation process at high sugar concentration.

PubMed

Arrizon, J; Gschaedler, A

2007-04-01

To study the effect of the addition of different nitrogen sources at high sugar concentration in the tequila fermentation process. Fermentations were performed at high sugar concentration (170 g l(-1)) using Agave tequilana Weber blue variety with and without added nitrogen from different sources (ammonium sulfate; glutamic acid; a mixture of ammonium sulfate and amino acids) during the exponential phase of growth. All the additions increased the fermentation rate and alcohol efficiency. The level of synthesis of volatile compounds depended on the source added. The concentration of amyl alcohols and isobutanol were decreased while propanol and acetaldehyde concentration increased. The most efficient nitrogen sources for fermentation rate were ammonium sulfate and the mixture of ammonium sulfate and amino acids. The level of volatile compounds produced depended upon types of nitrogen. The synthesis of some volatile compounds increased while others decreased with nitrogen addition. The addition of nitrogen could be a strategy for improving the fermentation rate and efficiency in the tequila fermentation process at high sugar Agave tequilana concentration. Furthermore, the sensory quality of the final product may change because the synthesis of the volatile compounds is modified.

Photoluminescence of etched SiC nanowires

NASA Astrophysics Data System (ADS)

Stewart, Polite D., Jr.; Rich, Ryan; Zerda, T. W.

2010-10-01

SiC nanowires were produced from carbon nanotubes and nanosize silicon powder in a tube furnace at temperatures between 1100^oC and 1350^oC. SiC nanowires had average diameter of 30 nm and very narrow size distribution. The compound possesses a high melting point, high thermal conductivity, and excellent wear resistance. The surface of the SiC nanowires after formation is covered by an amorphous layer. The composition of that layer is not fully understood, but it is believed that in addition to amorphous SiC it contains various carbon and silicon compounds, and SiO2. The objective of the research was to modify the surface structure of these SiC nanowires. Modification of the surface was done using the wet etching method. The etched nanowires were then analyzed using Fourier Transform Infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and photoluminescence (PL). FTIR and TEM analysis provided valid proof that the SiC nanowires were successfully etched. Also, the PL results showed that the SiC nanowire core did possess a fluorescent signal.

Effect of SiC addition to the characteristics of Al-11Zn-6.7Mg composite produced by squeeze casting for ballistic application

NASA Astrophysics Data System (ADS)

Adiputra, R. F.; Wijanarko, R.; Angela, I.; Sofyan, B. T.

2018-01-01

Aluminium composite material as an alternative to steel used in body of tactical vehicles has been studied. Addition of SiC was expected to have strengthening effect on the composite matrix therefore improving its ballistic performance. Composites of Al-11Zn-6.7Mg matrix and SiC strengthening particles with the fraction of 0, 10, and 15 vol. % were fabricated through squeeze casting process. Composite samples were then precipitation strengthened at 130 °C for 102 h to further improve their toughness. Final products were characterized by using chemical composition testing, optical microscopy, Scanning Electron Microscope - Energy Dispersive Spectroscopy (SEM-EDS) and quantitative metallography to calculate porosity, hardness test, impact test, and type III ballistic test in accordance with NIJ 0108.04 standard. The results showed that increase in SiC volume fraction from 0 to 10 and 15 vol. % managed to improve the hardness from 73 to 85 and 87 HRB, respectively, while on the other hand reduced the impact values from 12,278.69 to 11,290.35 and 9,924.54 J/m2. SEM-EDS observation confirmed the presence of Mg3Zn3Al2 intermetallic compound which formed during solidification and indicated the precipitation of MgZn2 precipitates during ageing. The ballistic testing demonstrated a promising result of the potential of Al-11Zn-6.7Mg composite strengthened by 15 vol. % SiC to withstand penetration of type III bullet (7.62 mm).

Efficient siRNA Delivery Using Novel Cell-Penetrating Peptide-siRNA Conjugate-Loaded Nanobubbles and Ultrasound.

PubMed

Xie, Xiangyang; Lin, Wen; Li, Mingyuan; Yang, Yang; Deng, Jianping; Liu, Hui; Chen, Ying; Fu, Xudong; Liu, Hong; Yang, Yanfang

2016-06-01

Because of the absence of tolerable and effective carriers for in vivo delivery, the applications of small interfering RNA (siRNA) in the clinic for therapeutic purposes have been limited. In this study, development of a novel siRNA delivery system based on ultrasound-sensitive nanobubbles (NBs, nano-sized echogenic liposomes) and cell-permeable peptides (CPPs) is described. A CPP-siRNA conjugate was entrapped in an NB, (CPP-siRNA)-NB, and the penetration of CPP-siRNA was temporally masked; local ultrasound stimulation triggered the release of CPP-siRNA from the NBs and activated its penetration. Subsequent research revealed that the (CPP-siRNA)-NBs had a mean particle size of 201 ± 2.05 nm and a siRNA entrapment efficiency >85%. In vitro release results indicated that >90% of the encapsulated CPP-siRNA was released from NBs in the presence of ultrasound, whereas <1.5% (30 min) was released in the absence of ultrasound. Cell experiments indicated higher cellular CPP-siRNA uptake of (CPP-siRNA)-NBs with ultrasound among the various formulations in human breast adenocarcinoma cells (HT-1080). Additionally, after systemic administration in mice, (CPP-siRNA)-NBs accumulated in the tumor, augmented c-myc silencing and delayed tumor progression. In conclusion, the application of (CPP-siRNA)-NBs with ultrasound may constitute an approach to selective targeted delivery of siRNA. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

On the Relation of Silicates and SiO Maser in Evolved Stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jiaming; Jiang, Biwei, E-mail: bjiang@bnu.edu.cn

2017-04-01

The SiO molecule is one of the candidates for the seed of silicate dust in the circumstellar envelope of evolved stars, but this opinion is challenged. In this work we investigate the relation of the SiO maser emission power and the silicate dust emission power. With both our own observation by using the PMO/Delingha 13.7 m telescope and archive data, a sample is assembled of 21 SiO v  = 1, J  = 2 − 1 sources and 28 SiO v  = 1, J  = 1 − 0 sources that exhibit silicate emission features in the ISO /SWS spectrum as well. The analysis of their SiO maser and silicatemore » emission power indicates a clear correlation, which is not against the hypothesis that the SiO molecules are the seed nuclei of silicate dust. On the other hand, no correlation is found between SiO maser and silicate crystallinity, which may imply that silicate crystallinity does not correlate with mass-loss rate.« less

Controlling contamination in Mo/Si multilayer mirrors by Si surface capping modifications

NASA Astrophysics Data System (ADS)

Malinowski, Michael E.; Steinhaus, Chip; Clift, W. Miles; Klebanoff, Leonard E.; Mrowka, Stanley; Soufli, Regina

2002-07-01

The performance of Mo/Si multilayer mirrors (MLMs) used to reflect UV (EUV) radiation in an EUV + hydrocarbon (NC) vapor environment can be improved by optimizing the silicon capping layer thickness on the MLM in order to minimize the initial buildup of carbon on MLMs. Carbon buildup is undesirable since it can absorb EUV radiation and reduce MLM reflectivity. A set of Mo/Si MLMs deposited on Si wafers was fabricated such that each MLM had a different Si capping layer thickness ranging form 2 nm to 7 nm. Samples from each MLM wafer were exposed to a combination of EUV light + (HC) vapors at the Advanced Light Source (ALS) synchrotron in order to determine if the Si capping layer thickness affected the carbon buildup on the MLMs. It was found that the capping layer thickness had a major influence on this 'carbonizing' tendency, with the 3 nm layer thickness providing the best initial resistance to carbonizing and accompanying EUV reflectivity loss in the MLM. The Si capping layer thickness deposited on a typical EUV optic is 4.3 nm. Measurements of the absolute reflectivities performed on the Calibration and Standards beamline at the ALS indicated the EUV reflectivity of the 3 nm-capped MLM was actually slightly higher than that of the normal, 4 nm Si-capped sample. These results show that he use of a 3 nm capping layer represents an improvement over the 4 nm layer since the 3 nm has both a higher absolute reflectivity and better initial resistance to carbon buildup. The results also support the general concept of minimizing the electric field intensity at the MLM surface to minimize photoelectron production and, correspondingly, carbon buildup in a EUV + HC vapor environment.

In situ formed Si nanoparticle network with micron-sized Si particles for lithium-ion battery anodes.

PubMed

Wu, Mingyan; Sabisch, Julian E C; Song, Xiangyun; Minor, Andrew M; Battaglia, Vincent S; Liu, Gao

2013-01-01

To address the significant challenges associated with large volume change of micrometer-sized Si particles as high-capacity anode materials for lithium-ion batteries, we demonstrated a simple but effective strategy: using Si nanoparticles as a structural and conductive additive, with micrometer-sized Si as the main lithium-ion storage material. The Si nanoparticles connected into the network structure in situ during the charge process, to provide electronic connectivity and structure stability for the electrode. The resulting electrode showed a high specific capacity of 2500 mAh/g after 30 cycles with high initial Coulombic efficiency (73%) and good rate performance during electrochemical lithiation and delithiation: between 0.01 and 1 V vs Li/Li(+).

Microstructure and properties of an Al-Ti-Cu-Si brazing alloy for SiC-metal joining

NASA Astrophysics Data System (ADS)

Dai, Chun-duo; Ma, Rui-na; Wang, Wei; Cao, Xiao-ming; Yu, Yan

2017-05-01

An Al-Ti-Cu-Si solid-liquid dual-phase alloy that exhibits good wettability and appropriate interfacial reaction with SiC at 500-600°C was designed for SiC-metal joining. The microstructure, phases, differential thermal curves, and high-temperature wetting behavior of the alloy were analyzed using scanning electron microscopy, X-ray diffraction analysis, differential scanning calorimetry, and the sessile drop method. The experimental results show that the 76.5Al-8.5Ti-5Cu-10Si alloy is mainly composed of Al-Al2Cu and Al-Si hypoeutectic low-melting-point microstructures (493-586°C) and the high-melting-point intermetallic compound AlTiSi (840°C). The contact angle, determined by high-temperature wetting experiments, is approximately 54°. Furthermore, the wetting interface is smooth and contains no obvious defects. Metallurgical bonding at the interface is attributable to the reaction between Al and Si in the alloy and ceramic, respectively. The formation of the brittle Al4C3 phase at the interface is suppressed by the addition of 10wt% Si to the alloy.

Use of a Si(Li) detector as β spectrometer.

PubMed

Dryák, P; Kovář, P

2014-05-01

The aim of this work is to demonstrate the capability of a Si(Li) detector for the measurement of β spectra, despite the energy absorption in air and in the Be window. A simple source holder fixes the source on the symmetry axis at 3mm from the detector window. The β-sources are produced by evaporation on a plastic backing plate. Absorbing materials between the source and the sensitive volume of the detector are 3 mm of air, a Be window, 0.1 μm Si and 20 nm of gold. A model of the detector was created for β spectra simulation using the MCNP 4A code. Experimental spectra of (14)C, (147)Pm, (204)Tl, (90)Sr/(90)Y were compared with simulated spectra. © 2013 Published by Elsevier Ltd.

Spent yeast as natural source of functional food additives

PubMed

Rakowska, Rita; Sadowska, Anna; Dybkowska, Ewa; Świderski, Franciszek

Spent yeasts are by-products arising from beer and wine production which over many years have been chiefly used as feed additives for livestock. They contain many valuable and bioactive substances which has thereby generated much interest in their exploitation. Up till now, the main products obtained from beer-brewing yeasts are β-glucans and yeast extracts. Other like foodstuffs include dried brewer’s yeast, where this is dried and the bitterness removed to be fit for human consumption as well as mannan-oligosaccharides hitherto used in the feed industry. β-glucans constitute the building blocks of yeast cell walls and can thus be used in human nutrition as dietary supplements or serving as food additives in functional foods. β-glucans products obtained via post-fermentation of beer also exhibit a high and multi-faceted biological activity where they improve the blood’s lipid profile, enhance immunological status and have both prebiotic and anti-oxidant properties. Yeast extracts are currently being used more and more to enhance flavour in foodstuffs, particularly for meat and its products. Depending on how autolysis is carried out, it is possible to design extracts of various meat flavours characteristic of specific meats. Many different flavour profiles can be created which may be additionally increased in combination with vegetable extracts. Within the food market, yeast extracts can appear in various guises such as liquids, pastes or powders. They all contain significant amounts of glutamic acid, 5’-GMP and 5’-IMP nucleotides together with various amino acids and peptides that act synergistically for enhancing the flavour of foodstuff products. Recent studies have demonstrated additional benefits of yeast extracts as valuable sources of amino acids and peptides which can be used in functional foods and dietary supplements. These products possess GRAS status (Generally Recognised As Safe) which thereby also adds further as to why they should be used

CVD growth and properties of boron phosphide on 3C-SiC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Padavala, Balabalaji; Frye, C. D.; Wang, Xuejing

Improving the crystalline quality of boron phosphide (BP) is essential for realizing its full potential in semiconductor device applications. In this study, 3C-SiC was tested as a substrate for BP epitaxy. BP films were grown on 3C-SiC(100)/Si, 3C-SiC(111)/Si, and 3C-SiC(111)/4H-SiC(0001) substrates in a horizontal chemical vapor deposition (CVD) system. Films were produced with good crystalline orientation and morphological features in the temperature range of 1000–1200 °C using a PH3+B2H6+H2 mixture. Rotational twinning was absent in the BP due to the crystal symmetry-matching with 3C-SiC. Confocal 3D Raman imaging of BP films revealed primarily uniform peak shift and peak widths acrossmore » the scanned area, except at defects on the surface. Synchrotron white beam X-ray topography showed the epitaxial relationship between BP and 3C-SiC was (100) <011>BP||(100) <011>3C-SiC and (111)View the MathML sourceBP||(111)View the MathML source3C-SiC. Scanning electron microscopy, Raman spectroscopy and X-ray diffraction analysis indicated residual tensile strain in the films and improved crystalline quality at temperatures below 1200 °C. These results indicated that BP properties could be further enhanced by employing high quality bulk 3C-SiC or 3C-SiC epilayers on 4H-SiC substrates.« less

Volume 3a - Area Source Methods - Additional Documents

EPA Pesticide Factsheets

Nonpoint (area) source emission reference materials from the Emissions Inventory Improvement Program (EIIP). Provides nonpoint source guidance on ammonia emissions from natural landscapes, fertilized soils, and nonagricultural sources.

Noise performance limits of advanced x-ray imagers employing poly-Si-based active pixel architectures

NASA Astrophysics Data System (ADS)

Koniczek, Martin; El-Mohri, Youcef; Antonuk, Larry E.; Liang, Albert; Zhao, Qihua; Jiang, Hao

2011-03-01

A decade after the clinical introduction of active matrix, flat-panel imagers (AMFPIs), the performance of this technology continues to be limited by the relatively large additive electronic noise of these systems - resulting in significant loss of detective quantum efficiency (DQE) under conditions of low exposure or high spatial frequencies. An increasingly promising approach for overcoming such limitations involves the incorporation of in-pixel amplification circuits, referred to as active pixel architectures (AP) - based on low-temperature polycrystalline silicon (poly-Si) thin-film transistors (TFTs). In this study, a methodology for theoretically examining the limiting noise and DQE performance of circuits employing 1-stage in-pixel amplification is presented. This methodology involves sophisticated SPICE circuit simulations along with cascaded systems modeling. In these simulations, a device model based on the RPI poly-Si TFT model is used with additional controlled current sources corresponding to thermal and flicker (1/f) noise. From measurements of transfer and output characteristics (as well as current noise densities) performed upon individual, representative, poly-Si TFTs test devices, model parameters suitable for these simulations are extracted. The input stimuli and operating-point-dependent scaling of the current sources are derived from the measured current noise densities (for flicker noise), or from fundamental equations (for thermal noise). Noise parameters obtained from the simulations, along with other parametric information, is input to a cascaded systems model of an AP imager design to provide estimates of DQE performance. In this paper, this method of combining circuit simulations and cascaded systems analysis to predict the lower limits on additive noise (and upper limits on DQE) for large area AP imagers with signal levels representative of those generated at fluoroscopic exposures is described, and initial results are reported.

Metastable Defect Formation at Microvoids Identified as a Source of Light-Induced Degradation in a-Si :H

NASA Astrophysics Data System (ADS)

Fehr, M.; Schnegg, A.; Rech, B.; Astakhov, O.; Finger, F.; Bittl, R.; Teutloff, C.; Lips, K.

2014-02-01

Light-induced degradation of hydrogenated amorphous silicon (a-Si :H), known as the Staebler-Wronski effect, has been studied by time-domain pulsed electron-paramagnetic resonance. Electron-spin echo relaxation measurements in the annealed and light-soaked state revealed two types of defects (termed type I and II), which can be discerned by their electron-spin echo relaxation. Type I exhibits a monoexponential decay related to indirect flip-flop processes between dipolar coupled electron spins in defect clusters, while the phase relaxation of type II is dominated by H1 nuclear spin dynamics and is indicative for isolated spins. We propose that defects are either located at internal surfaces of microvoids (type I) or are isolated and uniformly distributed in the bulk (type II). The concentration of both defect type I and II is significantly higher in the light-soaked state compared to the annealed state. Our results indicate that in addition to isolated defects, defects on internal surfaces of microvoids play a role in light-induced degradation of device-quality a-Si :H.

Secondary growth mechanism of SiGe islands deposited on a mixed-phase microcrystalline Si by ion beam co-sputtering.

PubMed

Ke, S Y; Yang, J; Qiu, F; Wang, Z Q; Wang, C; Yang, Y

2015-11-06

We discuss the SiGe island co-sputtering deposition on a microcrystalline silicon (μc-Si) buffer layer and the secondary island growth based on this pre-SiGe island layer. The growth phenomenon of SiGe islands on crystalline silicon (c-Si) is also investigated for comparison. The pre-SiGe layer grown on μc-Si exhibits a mixed-phase structure, including SiGe islands and amorphous SiGe (a-SiGe) alloy, while the layer deposited on c-Si shows a single-phase island structure. The preferential growth and Ostwald ripening growth are shown to be the secondary growth mechanism of SiGe islands on μc-Si and c-Si, respectively. This difference may result from the effect of amorphous phase Si (AP-Si) in μc-Si on the island growth. In addition, the Si-Ge intermixing behavior of the secondary-grown islands on μc-Si is interpreted by constructing the model of lateral atomic migration, while this behavior on c-Si is ascribed to traditional uphill atomic diffusion. It is found that the aspect ratios of the preferential-grown super islands are higher than those of the Ostwald-ripening ones. The lower lateral growth rate of super islands due to the lower surface energy of AP-Si on the μc-Si buffer layer for the non-wetting of Ge at 700 °C and the stronger Si-Ge intermixing effect at 730 °C may be responsible for this aspect ratio difference.

Coating of 6028 Aluminum Alloy Using Aluminum Piston Alloy and Al-Si Alloy-Based Nanocomposites Produced by the Addition of Al-Ti5-B1 to the Matrix Melt

NASA Astrophysics Data System (ADS)

El-Labban, Hashem F.; Abdelaziz, M.; Mahmoud, Essam R. I.

2014-10-01

The Al-12 pctSi alloy and aluminum-based composites reinforced with TiB2 and Al3Ti intermetallics exhibit good wear resistance, strength-to-weight ratio, and strength-to-cost ratio when compared to equivalent other commercial Al alloys, which make them good candidates as coating materials. In this study, structural AA 6028 alloy is used as the base material. Four different coating materials were used. The first one is Al-Si alloy that has Si content near eutectic composition. The second, third, and fourth ones are Al-6 pctSi-based reinforced with TiB2 and Al3Ti nano-particles produced by addition of Al-Ti5-B1 master alloy with different weight percentages (1, 2, and 3 pct). The coating treatment was carried out with the aid of GTAW process. The microstructures of the base and coated materials were investigated using optical microscope and scanning electron microscope equipped with EDX analyzer. Microhardness of the base material and the coated layer were evaluated using a microhardness tester. GTAW process results in almost sound coated layer on 6028 aluminum alloy with the used four coating materials. The coating materials of Al-12 pct Si alloy resulted in very fine dendritic Al-Si eutectic structure. The interface between the coated layer and the base metal was very clean. The coated layer was almost free from porosities or other defects. The coating materials of Al-6 pct Si-based mixed with Al-Ti5-B1 master alloy with different percentages (1, 2, and 3 pct), results in coated layer consisted of matrix of fine dendrite eutectic morphology structure inside α-Al grains. Many fine in situ TiAl3 and TiB2 intermetallics were precipitated almost at the grain boundary of α-Al grains. The amounts of these precipitates are increased by increasing the addition of Al-Ti5-B1 master alloy. The surface hardness of the 6028 aluminum alloy base metal was improved with the entire four used surface coating materials. The improvement reached to about 85 pct by the first type of

Oxidation of Ca-α-SiAlON Powders Prepared by Combustion Synthesis

PubMed Central

Li, Jinfu; Li, Zhongmin; Wang, Enhui; Wang, Zhanjun; Yin, Xiaowei; Zhang, Zuotai

2015-01-01

The oxidation of Ca-α-SiAlON synthesized by the combustion synthesis (CS) method with different additives was investigated in air atmosphere using thermogravimetric (TG) analysis in a temperature range from 1453 K to 1653 K. The experimental results indicated that oxidation was controlled by mixed chemical and diffusion steps. The oxidation products by XRD analysis were composed of SiO2 and CaAl2Si2O8 at low oxidation temperature, whereas the SiO2-Al2O3-CaO ternary glassy phase was formed at elevated temperature. The deviation of oxidation resistance from each sample may be due to the morphological difference brought about by different additive additions. This study reveals the effects of additives on the oxidation resistance of synthesized Ca-α-SiAlON powders. PMID:28793657

PIE of nuclear grade SiC/SiC flexural coupons irradiated to 10 dpa at LWR temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koyanagi, Takaaki; Katoh, Yutai

Silicon carbide fiber-reinforced SiC matrix (SiC/SiC) composites are being actively investigated for accident-tolerant core structures of light water reactors (LWRs). Owing to the limited number of irradiation studies previously conducted at LWR-coolant temperature, this study examined SiC/SiC composites following neutron irradiation at 230–340°C to 2.0 and 11.8 dpa in the High Flux Isotope Reactor. The investigated materials are chemical vapor infiltrated (CVI) SiC/SiC composites with three different reinforcement fibers. The fiber materials were monolayer pyrolytic carbon (PyC)-coated Hi-NicalonTM Type-S (HNS), TyrannoTM SA3 (SA3), and SCS-Ultra TM (SCS) SiC fibers. The irradiation resistance of these composites was investigated based on flexuralmore » behavior, dynamic Young’s modulus, swelling, and microstructures. There was no notable mechanical properties degradation of the irradiated HNS and SA3 SiC/SiC composites except for reduction of the Young’s moduli by up to 18%. The microstructural stability of these composites supported the absence of degradation. In addition, no progressive swelling from 2.0 to 11.8 dpa was confirmed for these composites. On the other hand, the SCS composite showed significant mechanical degradation associated with cracking within the fiber. This study determined that SiC/SiC composites with HNS or SA3 SiC/SiC fibers, a PyC interphase, and a CVI SiC matrix retain their properties beyond the lifetime dose for LWR fuel cladding at the relevant temperature.« less

Thermomechanical Performance of Si-Ti-C-O and Sintered SiC Fiber-Bonded Ceramics at High Temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matsunaga, Tadashi; Lin, Hua-Tay; Singh, Mrityunjay

2011-01-01

The stress-temperature-lifetime response of Si-Ti-C-O fiber-bonded ceramic (Tyrannohex ) and sintered SiC fiber-bonded ceramic (SA-Tyrannohex ) materials were investigated in air from 500 to 1150 C and 500 to 1400 C, respectively. The apparent threshold stress of Si-Ti-C-O fiber-bonded ceramic was about 175 MPa in the 500-1150 C temperature range. When the applied stress of the sintered SiC fiber-bonded ceramic was below an apparent threshold stress (e.g., ~225MPa) for tests conducted 1150 C, no failures were observed for lifetimes up to 1000h. In the case of sintered SiC fiber-bonded ceramic, at the temperature of 1300 C, the apparent threshold stressmore » decreased to 175 MPa. The decrease in strength seemed to be caused by grain growth which was confirmed from the SEM fractography. Both fiber-bonded ceramics exhibited much higher durability than a commercial SiC/SiC composite at temperatures above 500 C. In addition, results suggested that the sintered SiC fiber-bonded ceramic (SA-Tyrannohex) is more stable than a Hi-Nicalon/MI SiC composite with BN/SiC fiber coating at temperatures above 1300 C.« less

J-type Carbon Stars: A Dominant Source of 14 N-rich Presolar SiC Grains of Type AB

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Nan; Stephan, Thomas; Boehnke, Patrick

We report Mo isotopic data of 27 new presolar SiC grains, including 12 N-14-rich AB (N-14/N-15 > 440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS grains, which came from low-mass asymptotic giant branch (AGB) stars with large s-process isotope enhancements, with the AB2 grain data demonstrates that AB2 grains show near-solar isotopic compositions and lack s-process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of AB2 grains clearly exclude born-again AGB stars, where the intermediate neutron-capture process (i-process) takes place, as theirmore » stellar source. On the other hand, low-mass CO novae and early R-and J-type carbon stars show C-13 and N-14 excesses but no s-process enhancements and are thus potential stellar sources of AB2 grains. Because both early R-type carbon stars and CO novae are rare objects, the abundant J-type carbon stars (10%-15% of all carbon stars) are thus likely to be a dominant source of AB2 grains.« less

Total Ionizing Dose Effects on Ge Channel $p$FETs with Raised $${\\rm Si}_{0.55}{\\rm Ge}_{0.45}$$ Source/Drain

DOE PAGES

Wang, Liang; Zhang, En Xia; Schrimpf, Ronald D.; ...

2015-12-17

Here, the total ionizing dose response of Ge channel pFETs with raised Si 0.55Ge 0.45 source/drain is investigated under different radiation bias conditions. Threshold-voltage shifts and transconductance degradation are noticeable only for negative-bias (on state) irradiation, and are mainly due to negative bias-temperature instability (NBTI). Nonmonotonic leakage changes during irradiation are observed, which are attributed to the competition of radiation-induced field transistor leakage and S/D junction leakage.

Knowledge of Pest Resistance in SiC/BN/SiC Composites Improved

NASA Technical Reports Server (NTRS)

Thomas-Ogbuji, Linus U.

2002-01-01

Ceramic-matrix composites (CMC's) consisting of a silicon carbide matrix reinforced with boron-nitride- (BN-) coated silicon carbide (SiC) fibers are strong contenders for commercial and aerospace applications (in particular, the hot sections of high-performance turbine engines in advanced aircraft and generators). They have very good mechanical properties below approximately 600 C and above approximately 1000 C. Between those temperatures, however, the BN coating oxidizes easily, and the oxidation of the SiC matrix is too sluggish to seal off the composite with a protective layer of silica. In that temperature interval, the preferential oxidation of the BN weakens and embrittles the composite. That phenomenon, referred to as "pest" degradation, is the focus of this work, which aims to identify the causes of and remedies for pesting. Previous work established that pesting in Hi-Nicalon (Nippon Carbon Co., Ltd., Japan)/SiC composites was caused by a layer of free carbon that undermined the oxidation resistance of the BN. New work suggests that composites containing a source of carbon are prone to severe pesting and that those that are free of elemental carbon are resistant pesting. Pest resistance was assessed by exposing machined samples for 100 to 150 hr in an atmospheric burner rig at 600 to 1100 C, followed by a tensile fracture test to measure residual mechanical properties and by characterization of the interphase microstructure. Whether the elemental carbon came from intrinsic or extrinsic sources, its presence induced the tensile strength to drop by over 50 percent in the burner rig, with an even more severe loss of fracture strain. A likely mechanism by which burnoff of the carbon layer exposes the BN to accelerated flank attack by ambient oxidants is shown. The BN is replaced with borosilicates that attack the fiber, and ultimately with silica that embrittles the composites by rigidly bonding components. Thus, the study has shown that pesting can be

Precipitation Sequence of a SiC Particle Reinforced Al-Mg-Si Alloy Composite

NASA Astrophysics Data System (ADS)

Shen, Rujuan; Wang, Yihan; Guo, Baisong; Song, Min

2016-11-01

In this study, the precipitation sequence of a 5 vol.% SiC particles reinforced Al-1.12 wt.%Mg-0.77 wt.%Si alloy composite fabricated by traditional powder metallurgy method was investigated by transmission electron microscopy and hardness measurements. The results indicated that the addition of SiC reinforcements not only suppresses the initial aging stage but also influences the subsequent precipitates. The precipitation sequence of the composite aged at 175 °C can be described as: Guinier-Preston (G.P.) zone → β″ → β' → B', which was confirmed by high-resolution transmission electron microscopy. This work might provide the guidance for the design and fabrication of hardenable automobile body sheet by Al-based composites with enhanced mechanical properties.

Anisotropic selective etching between SiGe and Si

NASA Astrophysics Data System (ADS)

Ishii, Yohei; Scott-McCabe, Ritchie; Yu, Alex; Okuma, Kazumasa; Maeda, Kenji; Sebastian, Joseph; Manos, Jim

2018-06-01

In Si/SiGe dual-channel FinFETs, it is necessary to simultaneously control the etched amounts of SiGe and Si. However, the SiGe etch rate is higher than the Si etch rate in not only halogen plasmas but also physical sputtering. In this study, we found that hydrogen plasma selectively etches Si over SiGe. The result shows that the selectivity of Si over SiGe can be up to 38 with increasing Ge concentration in SiGe. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) results indicate that hydrogen selectively bonds with Si rather than with Ge in SiGe. During the etching, hydrogen-induced Si surface segregation is also observed. It is also observed that the difference in etched amount between SiGe and Si can be controlled from positive to negative values even in Si/SiGe dual-channel fin patterning while maintaining the vertical profiles. Furthermore, no plasma-induced lattice damage was observed by transmission electron microscopy for both Si and SiGe fin sidewalls.

Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiNx/SiNy multilayers

NASA Astrophysics Data System (ADS)

Jiang, Xiaofan; Ma, Zhongyuan; Yang, Huafeng; Yu, Jie; Wang, Wen; Zhang, Wenping; Li, Wei; Xu, Jun; Xu, Ling; Chen, Kunji; Huang, Xinfan; Feng, Duan

2014-09-01

Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiNx/SiNy multilayers with high on/off ratio of 109. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos, we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.

Bulk Thermoelectric Materials Reinforced with SiC Whiskers

NASA Astrophysics Data System (ADS)

Akao, Takahiro; Fujiwara, Yuya; Tarui, Yuki; Onda, Tetsuhiko; Chen, Zhong-Chun

2014-06-01

SiC whiskers have been incorporated into Zn4Sb3 compound as reinforcements to overcome its extremely brittle nature. The bulk samples were prepared by either hot-extrusion or hot-pressing techniques. The obtained products containing 1 vol.% to 5 vol.% SiC whiskers were confirmed to exhibit sound appearance, high density, and fine-grained microstructure. Mechanical properties such as the hardness and fracture resistance were improved by the addition of SiC whiskers, as a result of dispersion strengthening and microstructural refinement induced by a pinning effect. Furthermore, crack deflection and/or bridging/pullout mechanisms are invoked by the whiskers. Regarding the thermoelectric properties, the Seebeck coefficient and electrical resistivity values comparable to those of the pure compound are retained over the entire range of added whisker amount. However, the thermal conductivity becomes large with increasing amount of SiC whiskers because of the much higher conductivity of SiC relative to the Zn4Sb3 matrix. This results in a remarkable degradation of the dimensionless figure of merit in the samples with addition of SiC whiskers. Therefore, the optimum amount of SiC whiskers in the Zn4Sb3 matrix should be determined by balancing the mechanical properties and thermoelectric performance.

Investigating the addition of SiO₂-CaO-ZnO-Na₂O-TiO₂ bioactive glass to hydroxyapatite: Characterization, mechanical properties and bioactivity.

PubMed

Yatongchai, Chokchai; Placek, Lana M; Curran, Declan J; Towler, Mark R; Wren, Anthony W

2015-11-01

Hydroxyapatite (Ca10(PO4)6(OH)2) is widely investigated as an implantable material for hard tissue restoration due to its osteoconductive properties. However, hydroxyapatite in bulk form is limited as its mechanical properties are insufficient for load-bearing orthopedic applications. Attempts have been made to improve the mechanical properties of hydroxyapatite, by incorporating ceramic fillers, but the resultant composite materials require high sintering temperatures to facilitate densification, leading to the decomposition of hydroxyapatite into tricalcium phosphate, tetra-calcium phosphate and CaO phases. One method of improving the properties of hydroxyapatite is to incorporate bioactive glass particles as a second phase. These typically have lower softening points which could possibly facilitate sintering at lower temperatures. In this work, a bioactive glass (SiO2-CaO-ZnO-Na2O-TiO2) is incorporated (10, 20 and 30 wt%) into hydroxyapatite as a reinforcing phase. X-ray diffraction confirmed that no additional phases (other than hydroxyapatite) were formed at a sintering temperature of 560 ℃ with up to 30 wt% glass addition. The addition of the glass phase increased the % crystallinity and the relative density of the composites. The biaxial flexural strength increased to 36 MPa with glass addition, and there was no significant change in hardness as a function of maturation. The pH of the incubation media increased to pH 10 or 11 through glass addition, and ion release profiles determined that Si, Na and P were released from the composites. Calcium phosphate precipitation was encouraged in simulated body fluid with the incorporation of the bioactive glass phase, and cell culture testing in MC-3T3 osteoblasts determined that the composite materials did not significantly reduce cell viability. © The Author(s) 2015.

Mechanistic analysis of temperature-dependent current conduction through thin tunnel oxide in n+-polySi/SiO2/n+-Si structures

NASA Astrophysics Data System (ADS)

Samanta, Piyas

2017-09-01

We present a detailed investigation on temperature-dependent current conduction through thin tunnel oxides grown on degenerately doped n-type silicon (n+-Si) under positive bias ( VG ) on heavily doped n-type polycrystalline silicon (n+-polySi) gate in metal-oxide-semiconductor devices. The leakage current measured between 298 and 573 K and at oxide fields ranging from 6 to 10 MV/cm is primarily attributed to Poole-Frenkel (PF) emission of trapped electrons from the neutral electron traps located in the silicon dioxide (SiO2) band gap in addition to Fowler-Nordheim (FN) tunneling of electrons from n+-Si acting as the drain node in FLOating gate Tunnel OXide Electrically Erasable Programmable Read-Only Memory devices. Process-induced neutral electron traps are located at 0.18 eV and 0.9 eV below the SiO2 conduction band. Throughout the temperature range studied here, PF emission current IPF dominates FN electron tunneling current IFN at oxide electric fields Eox between 6 and 10 MV/cm. A physics based new analytical formula has been developed for FN tunneling of electrons from the accumulation layer of degenerate semiconductors at a wide range of temperatures incorporating the image force barrier rounding effect. FN tunneling has been formulated in the framework of Wentzel-Kramers-Brilloiun taking into account the correction factor due to abrupt variation of the energy barrier at the cathode/oxide interface. The effect of interfacial and near-interfacial trapped-oxide charges on FN tunneling has also been investigated in detail at positive VG . The mechanism of leakage current conduction through SiO2 films plays a crucial role in simulation of time-dependent dielectric breakdown of the memory devices and to precisely predict the normal operating field or applied floating gate (FG) voltage for lifetime projection of the devices. In addition, we present theoretical results showing the effect of drain doping concentration on the FG leakage current.

Additivity of the coefficient of thermal expansion in silicate optical fibers.

PubMed

Cavillon, M; Dragic, P D; Ballato, J

2017-09-15

A model that predicts the material additivity of the thermal expansion coefficient in the binary silicate glasses most commonly used for present (GeO 2 -SiO 2 , P 2 O 5 -SiO 2 , B 2 O 3 -SiO 2 , and Al 2 O 3 -SiO 2 ) and emerging (BaO-SiO 2 ) optical fibers is proposed. This model is based on a derivation of the expression for the coefficient of thermal expansion in isotropic solids, and gives direct insight on the parameters that govern its additivity in silicate glasses. Furthermore, a consideration of the local structural environment of the glass system is necessary to fully describe its additivity behavior in the investigated systems. This Letter is important for better characterizing and understanding of the impact of temperature and internal stresses on the behavior of optical fibers.

Strain and stability of ultrathin Ge layers in Si/Ge/Si axial heterojunction nanowires

DOE PAGES

Ross, Frances M.; Stach, Eric A.; Wen, Cheng -Yen; ...

2015-02-05

The abrupt heterointerfaces in the Si/Ge materials system presents useful possibilities for electronic device engineering because the band structure can be affected by strain induced by the lattice mismatch. In planar layers, heterointerfaces with abrupt composition changes are difficult to realize without introducing misfit dislocations. However, in catalytically grown nanowires, abrupt heterointerfaces can be fabricated by appropriate choice of the catalyst. Here we grow nanowires containing Si/Ge and Si/Ge/Si structures respectively with sub-1nm thick Ge "quantum wells" and we measure the interfacial strain fields using geometric phase analysis. Narrow Ge layers show radial strains of several percent, with a correspondingmore » dilation in the axial direction. Si/Ge interfaces show lattice rotation and curvature of the lattice planes. We conclude that high strains can be achieved, compared to what is possible in planar layers. In addition, we study the stability of these heterostructures under heating and electron beam irradiation. The strain and composition gradients are supposed to the cause of the instability for interdiffusion.« less

Development of Si/SiGe heterostructures

NASA Astrophysics Data System (ADS)

Hauenstein, R. J.; Veteran, J. L.; Young, M. H.

1991-01-01

New molecular beam epitaxy (MBE) materials growth and doping processes were developed for the fabrication of Si/SiGe heterostructure devices. These new materials processes are applied to the demonstration of cryogenic n-p-n Si/Si 1-x Gex/Si heterojunction bipolar transistors (HBT). This application has special significance as an enabling DoD technology for fast low noise, high performance readout and signal processing circuits for IR focal systems. Reliable, versatile methods were developed to grow very high quality Si/SiGe strained layer heterostructures and multilayers. In connection with this program methods were developed to dope the Si and SiGe with B, Sb and Ga. B and Sb were found to be the preferred dopants for p and n regions respectively, of the HBT devices. The test devices clearly displayed gain enhancement due to the heterojunction and provided useful gains from room temperature down to 10 K.

Undoped Si/SiGe Depletion-Mode Few-Electron Double Quantum Dots

NASA Astrophysics Data System (ADS)

Borselli, Matthew; Huang, Biqin; Ross, Richard; Croke, Edward; Holabird, Kevin; Hazard, Thomas; Watson, Christopher; Kiselev, Andrey; Deelman, Peter; Alvarado-Rodriguez, Ivan; Schmitz, Adele; Sokolich, Marko; Gyure, Mark; Hunter, Andrew

2011-03-01

We have successfully formed a double quantum dot in the sSi/SiGe material system without need for intentional dopants. In our design, a two-dimensional electron gas is formed in a strained silicon well by forward biasing a global gate. Lateral definition of quantum dots is established with reverse-biased gates with ~ 40 nm critical dimensions. Low-temperature capacitance and Hall measurements confirm electrons are confined in the Si-well with mobilities > 10 4 cm 2 / V - s . Further characterization identifies practical gate bias limits for this design and will be compared to simulation. Several double dot devices have been brought into the few-electron Coulomb blockade regime as measured by through-dot transport. Honeycomb diagrams and nonlinear through-dot transport measurements are used to quantify dot capacitances and addition energies of several meV. Sponsored by United States Department of Defense. Approved for Public Release, Distribution Unlimited.

Recent progress in Si thin film technology for solar cells

NASA Astrophysics Data System (ADS)

Kuwano, Yukinori; Nakano, Shoichi; Tsuda, Shinya

1991-11-01

Progress in Si thin film technology 'specifically amorphous Si (a-Si) and polycrystalline Si (poly-Si) thin film' for solar cells is summarized here from fabrication method, material, and structural viewpoints. In addition to a-Si, primary results on poly-Si thin film research are discussed. Various applications for a-Si solar cells are mentioned, and consumer applications and a-Si solar cell photovoltaic systems are introduced. New product developments include see-through solar cells, solar cell roofing tiles, and ultra-light flexible solar cells. As for new systems, air conditioning equipment powered by solar cells is described. Looking to the future, the proposed GENESIS project is discussed.

Temperature dependence of 63Ni-Si betavoltaic microbattery.

PubMed

Yunpeng, Liu; Xiao, Guo; Zhangang, Jin; Xiaobin, Tang

2018-05-01

This paper theoretically presented the temperature effects on the 63 Ni-Si betavoltaic microbattery irradiated by a source with different thicknesses and activity densities at a temperature range 170-340K. Temperature dependences of the monolayer and interbedded 63 Ni-Si betavoltaics at 213.15-333.15K were tested with respect to calculations. Results showed that the higher the thickness, activity density, and average energy of the source, the lower is the betavoltaic performance responds to temperature. With the increase in temperature, the V oc and P max of the upper, lower, and interbedded betavoltaics decreased linearly at low temperatures and decreased exponentially at high temperatures in the experiment. As predicted, the measured V oc and P max sensitivities of the lower betavoltaic with 4.90mCi/cm 2 63 Ni, -2.230mV/K and -1.132%, respectively, were lower than those with 1.96mCi/cm 2 63 Ni, -2.490mV/K and -1.348%, respectively. Compared with the calculated results, the prepared betavoltaics had lower V oc sensitivity and higher P max sensitivity. In addition, the measured V oc sensitivity of the interbedded betavoltaic in series is equal to the sum of those of the upper and lower ones as predicted. Moreover, the measured P max sensitivity of the interbedded betavoltaic is equal to the average of those of the two monolayers. Copyright © 2018 Elsevier Ltd. All rights reserved.

Subeutectic Synthesis of Epitaxial Si-NWs with Diverse Catalysts Using a Novel Si Precursor

PubMed Central

2010-01-01

The applicability of a novel silicon precursor with respect to reasonable nanowire (NW) growth rates, feasibility of epitaxial NW growth and versatility with respect to diverse catalysts was investigated. Epitaxial growth of Si-NWs was achieved using octochlorotrisilane (OCTS) as Si precursor and Au as catalyst. In contrast to the synthesis approach with SiCl4 as precursor, OCTS provides Si without the addition of H2. By optimizing the growth conditions, effective NW synthesis is shown for alternative catalysts, in particular, Cu, Ag, Ni, and Pt with the latter two being compatible to complementary metal-oxide-semiconductor technology. As for these catalysts, the growth temperatures are lower than the lowest liquid eutectic; we suggest that the catalyst particle is in the solid state during NW growth and that a solid-phase diffusion process, either in the bulk, on the surface, or both, must be responsible for NW nucleation. PMID:20843058

Technique development for modulus, microcracking, hermeticity, and coating evaluation capability characterization of SiC/SiC tubes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Xunxiang; Ang, Caen K.; Singh, Gyanender P.

Driven by the need to enlarge the safety margins of nuclear fission reactors in accident scenarios, research and development of accident-tolerant fuel has become an important topic in the nuclear engineering and materials community. A continuous-fiber SiC/SiC composite is under consideration as a replacement for traditional zirconium alloy cladding owing to its high-temperature stability, chemical inertness, and exceptional irradiation resistance. An important task is the development of characterization techniques for SiC/SiC cladding, since traditional work using rectangular bars or disks cannot directly provide useful information on the properties of SiC/SiC composite tubes for fuel cladding applications. At Oak Ridge Nationalmore » Laboratory, experimental capabilities are under development to characterize the modulus, microcracking, and hermeticity of as-fabricated, as-irradiated SiC/SiC composite tubes. Resonant ultrasound spectroscopy has been validated as a promising technique to evaluate the elastic properties of SiC/SiC composite tubes and microcracking within the material. A similar technique, impulse excitation, is efficient in determining the basic mechanical properties of SiC bars prepared by chemical vapor deposition; it also has potential for application in studying the mechanical properties of SiC/SiC composite tubes. Complete evaluation of the quality of the developed coatings, a major mitigation strategy against gas permeation and hydrothermal corrosion, requires the deployment of various experimental techniques, such as scratch indentation, tensile pulling-off tests, and scanning electron microscopy. In addition, a comprehensive permeation test station is being established to assess the hermeticity of SiC/SiC composite tubes and to determine the H/D/He permeability of SiC/SiC composites. This report summarizes the current status of the development of these experimental capabilities.« less

Si Nanocrystal-Embedded SiO x nanofoils: Two-Dimensional Nanotechnology-Enabled High Performance Li Storage Materials.

PubMed

Yoo, Hyundong; Park, Eunjun; Bae, Juhye; Lee, Jaewoo; Chung, Dong Jae; Jo, Yong Nam; Park, Min-Sik; Kim, Jung Ho; Dou, Shi Xue; Kim, Young-Jun; Kim, Hansu

2018-05-02

Silicon (Si) based materials are highly desirable to replace currently used graphite anode for lithium ion batteries. Nevertheless, its usage is still a big challenge due to poor battery performance and scale-up issue. In addition, two-dimensional (2D) architectures, which remain unresolved so far, would give them more interesting and unexpected properties. Herein, we report a facile, cost-effective, and scalable approach to synthesize Si nanocrystals embedded 2D SiO x nanofoils for next-generation lithium ion batteries through a solution-evaporation-induced interfacial sol-gel reaction of hydrogen silsesquioxane (HSiO 1.5 , HSQ). The unique nature of the thus-prepared centimeter scale 2D nanofoil with a large surface area enables ultrafast Li + insertion and extraction, with a reversible capacity of more than 650 mAh g -1 , even at a high current density of 50 C (50 A g -1 ). Moreover, the 2D nanostructured Si/SiO x nanofoils show excellent cycling performance up to 200 cycles and maintain their initial dimensional stability. This superior performance stems from the peculiar nanoarchitecture of 2D Si/SiO x nanofoils, which provides short diffusion paths for lithium ions and abundant free space to effectively accommodate the huge volume changes of Si during cycling.

Characteristics of Commercial SiC and Synthetic SiC as an Aggregate in Geopolymer Composites

NASA Astrophysics Data System (ADS)

Irfanita, R.; Afifah, K. N.; Asrianti; Subaer

2017-03-01

This main objective of this study is to investigate the effect silicon carbide (SiC) as an aggregate on the mechanical strength and microstructure of the geopolymer composites. The geopolymers binder were produced by using alkaline activation method of metakaolin and cured at 70oC for 2 hours. In this study commercial and synthetic SiC were used as aggregate to produce composite structure. Synthetic SiC was produced from rice husk ash and coconut shell carbon calcined at 750oC for 2 hours. The addition of SiC in geopolymers paste was varied from 0.25g, 0.50g to 0.75g to form geopolymers composites. The chemical compositions and crystallinity level of SiC and the resulting composites were measured by means of Rigaku MiniFlexII X-Ray Diffraction (XRD). The microstructure of SiC and the composites were examined by using Tescan Vega3SB Scanning Electron Microscopy (SEM). The physical and mechanical properties of the samples were determined based on apparent porosity, bulk density, and three bending flexural strength measurements. The results showed that the commercial and synthetic SiC were effectively produced geopolymers composites with different microstructure, physical and mechanical strength.

Enhancement of red emission intensity of Ca2Al2SiO7:Eu3+ phosphor by MoO3 doping or excess SiO2 addition for application to white LEDs

NASA Astrophysics Data System (ADS)

Jiao, H. Y.; LiMao, C. R.; Chen, Q.; Wang, P. Y.; Cai, R. C.

2018-01-01

Ca1.86Al2(Si1-xMox)O7:0.14Eu3+ and Ca1.86Al2Si1+yO7+2y:0.14 Eu3+ were synthesized by solid-state reaction. X-ray powder diffraction, excitation and emission spectra were used to investigate their structures and photoluminescence properties. The results shows that the phosphor Ca1.86Al2SiO7:0.14Eu3+ cannot be excited efficiently by light of 393 nm. The introduced Mo ion does not change the position of the excitation peak, but increases both the absorption at 400nm and the emission intensity of Eu3+. The intense red emitting phosphor Ca1.86Al2(Si0.95Mo0.05)O7:0.14Eu3+ was obtained, which has 67% enhanced luminous intensity compared to that of the undoped sample Ca1.86Al2SiO7:0.14Eu3+. Otherwise, SiO2 excess of non-stoichiometric phosphors Ca1.86Al2Si1+yO7+2y:0.14Eu3+ showed the characteristic pattern of a tetragonal structure with a small SiO2 concentration. The optimal phosphor of Ca1.86Al2Si1.1O7.2:0.14Eu3+ has a luminous intensity about two times higher than that of the original stoichiometric phosphor Ca1.86Al2SiO7:0.14Eu3+. We confirmed that the photoluminescence intensity of the obtained phosphors is fairly enhanced by excessive SiO2. The mechanism of this photoluminescence enhancement is discussed in this paper.

The Stellar Imager (SI) Project: Resolving Stellar Surfaces, Interiors, and Magnetic Activity

NASA Technical Reports Server (NTRS)

Carpenter, Kenneth G.; Schrijver, K.; Karovska, M.

2007-01-01

The Stellar Imager (SI) is a UV/Optical. Space-Based Interferometer designed to enable 0.1 milli-arcsec (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of SI will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. The science of SI focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. Its prime goal is to enable long-term forecasting of solar activity and the space weather that it drives. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. In this paper we discuss the science goals, technology needs, and baseline design of the SI mission.

A new direct growth method of graphene on Si-face of 6H-SiC by synergy of the inner and external carbon sources

NASA Astrophysics Data System (ADS)

Yang, Zhiyuan; Xu, Shicai; Zhao, Lili; Zhang, Jing; Wang, Zhengping; Chen, Xiufang; Cheng, Xiufeng; Yu, Fapeng; Zhao, Xian

2018-04-01

Graphene is a promising two-dimensional material that has possible application in various disciplines, due to its super properties, including high carrier mobility, chemical stability, and optical transparency etc. In this paper, we report an inner and external carbon synergy (IECS) method to grow graphene on Si-face of 6H-SiC. This method combined the advantages of chemical vapor deposition (CVD) and traditional epitaxial growth (EG) based on silicon carbide, which providing a feasible approach for growing graphene on the SiC substrates. The graphene was synthesized within just 3 min, which was more than one order of magnitude faster than the graphene grown on 6H-SiC substrates by the traditional EG method. The growth temperature was ∼200 °C lower than the EG process. The directly grown graphene maintained the compatibility with the semiconductor technique, which is benefit for use in graphene-based microelectronic devices.

Calcium addition at the Hubbard Brook Experimental Forest increases sugar storage, antioxidant activity and cold tolerance in native red spruce (Picea rubens)

Treesearch

Joshua M. Halman; Paul G. Schaberg; Gary J. Hawley; Christopher Eagar

2008-01-01

In fall (November 2005) and winter (February 2006), we collected current-year foliage of native red spruce (Picea rubens Sarg.) growing in a reference watershed and in a watershed treated in 1999 with wollastonite (CaSiO3, a slow-release calcium source) to simulate preindustrial soil calcium concentrations (Ca-addition...

SiC Seeded Crystal Growth

NASA Astrophysics Data System (ADS)

Glass, R. C.; Henshall, D.; Tsvetkov, V. F.; Carter, C. H., Jr.

1997-07-01

The availability of relatively large (30 mm) SiC wafers has been a primary reason for the renewed high level of interest in SiC semiconductor technology. Projections that 75 mm SiC wafers will be available in 2 to 3 years have further peaked this interest. Now both 4H and 6H polytypes are available, however, the micropipe defects that occur to a varying extent in all wafers produced to date are seen by many as preventing the commercialization of many types of SiC devices, especially high current power devices. Most views on micropipe formation are based around Frank's theory of a micropipe being the hollow core of a screw dislocation with a huge Burgers vector (several times the unit cell) and with the diameter of the core having a direct relationship with the magnitude of the Burgers vector. Our results show that there are several mechanisms or combinations of these mechanisms which cause micropipes in SiC boules grown by the seeded sublimation method. Additional considerations such as polytype variations, dislocations and both impurity and diameter control add to the complexity of producing high quality wafers. Recent results at Cree Research, Inc., including wafers with micropipe densities of less than 1 cm - 2 (with 1 cm2 areas void of micropipes), indicate that micropipes will be reduced to a level that makes high current devices viable and that they may be totally eliminated in the next few years. Additionally, efforts towards larger diameter high quality substrates have led to production of 50 mm diameter 4H and 6H wafers for fabrication of LEDs and the demonstration of 75 mm wafers. Low resistivity and semi-insulating electrical properties have also been attained through improved process and impurity control. Although challenges remain, the industry continues to make significant progress towards large volume SiC-based semiconductor fabrication.

Processing and Properties of SiC/MoSi2-SiC Composites Fabricated by Melt Infiltration

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.; Hebsur, Mohan G.

2000-01-01

Hi-Nicalon SiC fiber reinforced MoSi2-SiC matrix composites (SiC/MoSi2-SiC) have been fabricated by the melt infiltration approach. The composite consists of approximately 60 vol%, 2-D woven BN/SiC coated Hi-Nicalon SiC fibers and approximately 40 vol% MoSi2-SiC matrix. The room temperature tensile properties and thermal conductivity of the SiC/MoSi2-SiC composites were measured and compared with those of the melt infiltrated SiC/SiC composites. The influence oi fiber architecture on tensile properties was also evaluated. Results indicate that the primary modulus, stress corresponding to deviation from linearity, and transverse thermal conductivity values for the SiC/MoSi2-SiC composites are significantly lower than those for the SiC/SiC composites. Microcracking of the matrix due to the large difference in thermal expansion between MoSi2 and SiC appears to be the reason for the lower matrix dominated properties of SiC/MoSi2-SiC composites.

Bose-Einstein correlations in Si + Al and Si + Au collisions at 14.6A GeV/c

NASA Technical Reports Server (NTRS)

Abbott, T.; Akiba, Y.; Beavis, D.; Bloomer, M. A.; Bond, P. D.; Chasman, C.; Chen, Z.; Chu, Y. Y.; Cole, B. A.; Costales, J. B.

1992-01-01

The E802 Spectrometer at the Brookhaven Alternating Gradient Synchrotron has been used to measure the correlation in relative momentum between like-sign pions emitted in central Si + Al and Si + Au collisions at 14.6A GeV/c. Data are presented in terms of the correlation function for both identified pi(-) and pi(+) pairs near the nucleon-nucleon center-of-mass rapidity. All parametrizations of the correlation function are consistent with a spherically symmetric source of rms radius 3.5 +/- 0.4 fm and lifetime fm/c.

Nitriding kinetics of Si-SiC powder mixtures as simulations of reaction bonded Si3N4-SiC composites

NASA Technical Reports Server (NTRS)

Lightfoot, A.; Sheldon, B. W.; Flint, J. H.; Haggerty, J. S.

1989-01-01

The nitriding kinetics of Si and Si plus SiC powder mixtures were studied to simulate the fabrication of RBSN-SiC ceramic matrix composites. Very clean, assynthesized, and solvent-exposed powders were studied; C-rich and Si-rich SiC 0.04-0.05 micron diameter powders were mixed in varying concentrations with SiH4-derived 0.2-0.3 micron diameter Si powder. Complete nitridation is achieved with C-rich SiC powders in 140 min at 1250 C, and in the centers of Si-rich SiC powders in 15 min. The effects on the incubation periods, fast reaction periods, and slow reaction periods that characterize these nitriding processes were studied to explain unusual reverse reaction gradients and other effects of contamination.

Nanocarriers for delivery of siRNA and co-delivery of siRNA and other therapeutic agents.

PubMed

Zhao, Jing; Feng, Si-Shen

2015-07-01

A major problem in cancer treatment is the multidrug resistance. siRNA inhibitors have great advantages to solve the problem, if the bottleneck of their delivery could be well addressed by the various nanocarriers. Moreover, co-delivery of siRNA together with the various anticancer agents in one nanocarrier may maximize their additive or synergistic effect. This review provides a comprehensive summary on the state-of-the-art of the nanocarriers, which may include prodrugs, micelles, liposomes, dendrimers, nanohydrogels, solid lipid nanoparticles, nanoparticles of biodegradable polymers and nucleic acid nanocarriers for delivery of siRNA and co-delivery of siRNA together with anticancer agents with focus on synthesis of the nanocarrier materials, design and characterization, in vitro and in vivo evaluation, and prospect and challenges of nanocarriers.

Elemental boron-doped p(+)-SiGe layers grown by molecular beam epitaxy for infrared detector applications

NASA Technical Reports Server (NTRS)

Lin, T. L.; George, T.; Jones, E. W.; Ksendzov, A.; Huberman, M. L.

1992-01-01

SiGe/Si heterojunction internal photoemission (HIP) detectors have been fabricated utilizing molecular beam epitaxy of p(+)-SiGe layers on p(-)-Si substrates. Elemental boron from a high-temperature effusion cell was used as the dopant source during MBE growth, and high doping concentrations have been achieved. Strong infrared absorption, mainly by free-carrier absorption, was observed for the degenerately doped SiGe layers. The use of elemental boron as the dopant source allows a low MBE growth temperature, resulting in improved crystalline quality and smooth surface morphology of the Si(0.7)Ge(0.3) layers. Nearly ideal thermionic emission dark current characteristics have been obtained. Photoresponse of the HIP detectors in the long-wavelength infrared regime has been demonstrated.

Selective epitaxial growth properties and strain characterization of Si1- x Ge x in SiO2 trench arrays

NASA Astrophysics Data System (ADS)

Koo, Sangmo; Jang, Hyunchul; Ko, Dae-Hong

2017-04-01

In this study, we investigated the formation of a Si1- x Ge x fin structure in SiO2 trench arrays via an ultra-high-vacuum chemical-vapor deposition (UHV-CVD) selective epitaxial growth (SEG) process. Defect generation and microstructures of Si1- x Ge x fin structures with different Ge concentrations ( x = 0.2, 0.3 and 0.45) were examined. In addition, the strain evolution of a Si1- x Ge x fin structure was analyzed by using reciprocal space mapping (RSM). An (111) facet was formed from the Si1- x Ge x epi-layer and SiO2 trench wall interface to minimize the interface and the surface energy. The Si1- x Ge x fin structures were fully relaxed along the direction perpendicular to the trenches regardless of the Ge concentration. On the other hand, the fin structures were fully or partially strained along the direction parallel to the trenches depending on the Ge concentration: fully strained Si0.8Ge0.2 and Si0.7Ge0.3, and a Si0.55Ge0.45 strain-relaxed buffer. We further confirmed that the strain on the Si1- x Ge x fin structures remained stable after oxide removal and H2/N2 post-annealing.

Epitaxial growth and characterization of Si/NiSi 2/Si(111) heterostructures

NASA Astrophysics Data System (ADS)

Rizzi, Angela; Förster, A.; Lüth, H.; Slijkerman, W.

1989-04-01

Si/NiSi 2/Si(111) heterostructures are grown under UHV conditions. The well known "template" method is used to produce the epitaxial NiSi 2 interlayer. On top of the suicide, the silicon epitaxial growth is obtained by means of gas phase reaction of SiH 4 at a surface temperature of 500° C. The Si growth rate is strongly enhanced by predissociation of SiH 4 using a hot tungsten filament in the vicinity of the surface. The single steps of the growth are followed in-situ by means of AES, HREELS and LEED analysis. Ex-situ high resolution RBS analysis is also applied for characterization.

The Addition of Several Mineral Sources on Growing Media of Fluorescent Pseudomonad for the Biosynthesis of Hydrogen Cyanide

NASA Astrophysics Data System (ADS)

Advinda, L.; Fifendy, M.; Anhar, A.

2018-04-01

All Fluorescent pseudomonad is a group of rhyzobacteria which these days often utilized on plant disease control. The growing media is an absolute requirement which needs to be considered for the growth and cultivation of bacteria. The mineral source contained in growing media of bacteria may affect the production of hydrogen cyanide compound. The objectives of the research were to obtain the best source of minerals for biosynthesis of cyanide acid compounds by fluorescent pseudomonad isolates PfPj1, PfPb1, PfPj2, Kd7, Cas, Cas3, and LAHp2. This research is a qualitative experimental research including observation of hydrogen cyanide compound produced after the growing media of fluorescent pseudomonad bacteria added with several mineral sources. The treatments were given: A = ZnSO4.7H2O 0.5 mM addition, B = CoCl2.6H2O 0.5 mM addition, and C = Fe2SO4.7H2O 0.5 mM addition. From the result of the research, it was concluded that the addition of ZnSO4.7H2O mineral resources on the growing media of fluorescent pseudomonad isolate Cas and Cas3 produced the best hydrogen cyanide. Whereas addition of CoCl2.6H2O mineral source on the growing media showed poor hydrogen cyanide production for all fluorescent pseudomonad isolates

Microstructural evolution during quenching and partitioning of 0.2C-1.5Mn-1.3Si steels with Cr or Ni additions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pierce, Dean T.; Coughlin, D. R.; Clarke, Kester D.

Here, the influence of Cr and Ni additions and quench and partition (Q&P) processing parameters on the microstructural development, including carbide formation and austenite retention during Q&P, was studied in two steels with a base composition of 0.2C-1.5Mn-1.3Si wt.% and additions of 1.5 wt.% Cr (1.5Cr) or Ni (1.5Ni). Additions of 1.5 wt.% Cr significantly slowed the kinetics of austenite decomposition relative to the 1.5Ni alloy at all partitioning temperatures, promoting greater austenite retention, lower retained austenite carbon (C) contents, and reduced sensitivity of the retained austenite amounts to processing variables. In the 1.5Cr alloy after partitioning at 400 °Cmore » for 300 s, η-carbides were identified by transmission electron microscopy (TEM) and atom probe tomography (APT) revealed no significant enrichment of substitutional elements in the carbides. In the 1.5Ni alloy after partitioning at 450 °C for 300 s, both plate-like and globular carbides were observed by TEM. APT analysis of the globular carbides clearly revealed significant Si rejection and Mn enrichment. Mössbauer effect spectroscopy was used to quantify the amount of carbides after Q&P. In general, carbide amounts below ~0.3% of Fe were measured in both alloys after partitioning for short times (10 s), irrespective of quench or partitioning temperature, which corresponds to a relatively small portion of the bulk C. With increasing partitioning time, carbide amounts remained approximately constant or increased, depending on the alloy, quench temperature, and/or partitioning temperature.« less

Microstructural evolution during quenching and partitioning of 0.2C-1.5Mn-1.3Si steels with Cr or Ni additions

DOE PAGES

Pierce, Dean T.; Coughlin, D. R.; Clarke, Kester D.; ...

2018-03-08

Here, the influence of Cr and Ni additions and quench and partition (Q&P) processing parameters on the microstructural development, including carbide formation and austenite retention during Q&P, was studied in two steels with a base composition of 0.2C-1.5Mn-1.3Si wt.% and additions of 1.5 wt.% Cr (1.5Cr) or Ni (1.5Ni). Additions of 1.5 wt.% Cr significantly slowed the kinetics of austenite decomposition relative to the 1.5Ni alloy at all partitioning temperatures, promoting greater austenite retention, lower retained austenite carbon (C) contents, and reduced sensitivity of the retained austenite amounts to processing variables. In the 1.5Cr alloy after partitioning at 400 °Cmore » for 300 s, η-carbides were identified by transmission electron microscopy (TEM) and atom probe tomography (APT) revealed no significant enrichment of substitutional elements in the carbides. In the 1.5Ni alloy after partitioning at 450 °C for 300 s, both plate-like and globular carbides were observed by TEM. APT analysis of the globular carbides clearly revealed significant Si rejection and Mn enrichment. Mössbauer effect spectroscopy was used to quantify the amount of carbides after Q&P. In general, carbide amounts below ~0.3% of Fe were measured in both alloys after partitioning for short times (10 s), irrespective of quench or partitioning temperature, which corresponds to a relatively small portion of the bulk C. With increasing partitioning time, carbide amounts remained approximately constant or increased, depending on the alloy, quench temperature, and/or partitioning temperature.« less

Auger-electron diffraction in the low kinetic-energy range: The Si(111)7×7 surface reconstruction and Ge/Si interface formation

NASA Astrophysics Data System (ADS)

de Crescenzi, M.; Gunnella, R.; Bernardini, R.; de Marco, M.; Davoli, I.

1995-07-01

We have investigated the Auger-electron diffraction (AED) of the L2,3VV Auger line of the clean 7×7 reconstructed Si(111) surface and the Ge/Si interface formed after a few monolayers (ML) of Ge deposition. The experimental AED in the low kinetic-energy regime has been interpreted within the framework of a multiple-scattering theory. The comparison of the AED data taken using both the x-ray source and an electron source evidences that the incident beam plays a negligible role when the experimental conditions require the use of an angular detector. The evolution of the Ge/Si(111) interface is studied by monitoring the intensity anisotropy of the Auger peaks of the two elements at room temperature (RT) and at 400 °C annealing temperature of the substrate. The evolution of the growth mechanism underlying the Ge/Si interface formation has been studied by exploiting the very low electron escape depth of this technique (<=5 Å). While at RT two monolayers of Ge deposition appear uniform and amorphous, the successive annealing induces an intermixing and a recrystallization only in the first two layers of the interface without any further interdiffusion. Furthermore, a Stranski-Krastanow growth mode has been deduced after deposition of 4 ML of Ge on a clean Si sample kept at 400 °C.

Design of Strain-Engineered GeSn/GeSiSn Quantum Dots for Mid-IR Direct Bandgap Emission on Si Substrate

NASA Astrophysics Data System (ADS)

Al-Saigh, Reem; Baira, Mourad; Salem, Bassem; Ilahi, Bouraoui

2018-06-01

Strain-engineered self-assembled GeSn/GeSiSn quantum dots in Ge matrix have been numerically investigated aiming to study their potentiality towards direct bandgap emission in the mid-IR range. The use of GeSiSn alloy as surrounding media for GeSn quantum dots (QD) allows adjusting the strain around the QD through the variation of Si and/or Sn composition. Accordingly, the lattice mismatch between the GeSn quantum dots and the GeSiSn surrounding layer has been tuned between - 2.3 and - 4.5% through the variation of the Sn barrier composition for different dome-shaped QD sizes. The obtained results show that the emission wavelength, fulfilling the specific QD directness criteria, can be successively tuned over a broad mid-IR range from 3 up to7 μm opening new perspectives for group IV laser sources fully integrated in Si photonic systems for sensing applications.

SiNOI and AlGaAs-on-SOI nonlinear circuits for continuum generation in Si photonics

NASA Astrophysics Data System (ADS)

El Dirani, Houssein; Monat, Christelle; Brision, Stéphane; Olivier, Nicolas; Jany, Christophe; Letartre, Xavier; Pu, Minhao; Girouard, Peter D.; Hagedorn Frandsen, Lars; Semenova, Elizaveta; Katsuo Oxenløwe, Leif; Yvind, Kresten; Sciancalepore, Corrado

2018-02-01

In this communication, we report on the design, fabrication, and testing of Silicon Nitride on Insulator (SiNOI) and Aluminum-Gallium-Arsenide (AlGaAs) on silicon-on-insulator (SOI) nonlinear photonic circuits for continuum generation in Silicon (Si) photonics. As recently demonstrated, the generation of frequency continua and supercontinua can be used to overcome the intrinsic limitations of nowadays silicon photonics notably concerning the heterogeneous integration of III-V on SOI lasers for datacom and telecom applications. By using the Kerr nonlinearity of monolithic silicon nitride and heterointegrated GaAs-based alloys on SOI, the generation of tens or even hundreds of new optical frequencies can be obtained in dispersion tailored waveguides, thus providing an all-optical alternative to the heterointegration of hundreds of standalone III-V on Si lasers. In our work, we present paths to energy-efficient continua generation on silicon photonics circuits. Notably, we demonstrate spectral broadening covering the full C-band via Kerrbased self-phase modulation in SiNOI nanowires featuring full process compatibility with Si photonic devices. Moreover, AlGaAs waveguides are heterointegrated on SOI in order to dramatically reduce (x1/10) thresholds in optical parametric oscillation and in the power required for supercontinuum generation under pulsed pumping. The manufacturing techniques allowing the monolithic co-integration of nonlinear functionalities on existing CMOS-compatible Si photonics for both active and passive components will be shown. Experimental evidence based on self-phase modulation show SiNOI and AlGaAs nanowires capable of generating wide-spanning frequency continua in the C-Band. This will pave the way for low-threshold power-efficient Kerr-based comb- and continuum- sources featuring compatibility with Si photonic integrated circuits (Si-PICs).

Sub-barrier fusion of Si+Si systems

NASA Astrophysics Data System (ADS)

Colucci, G.; Montagnoli, G.; Stefanini, A. M.; Bourgin, D.; Čolović, P.; Corradi, L.; Courtin, S.; Faggian, M.; Fioretto, E.; Galtarossa, F.; Goasduff, A.; Haas, F.; Mazzocco, M.; Scarlassara, F.; Stefanini, C.; Strano, E.; Urbani, M.; Szilner, S.; Zhang, G. L.

2017-11-01

The near- and sub-barrier fusion excitation function has been measured for the system 30Si+30Si at the Laboratori Nazionali di Legnaro of INFN, using the 30Si beam of the XTU Tandem accelerator in the energy range 47 - 90 MeV. A set-up based on a beam electrostatic deflector was used for detecting fusion evaporation residues. The measured cross sections have been compared to previous data on 28Si+28Si and Coupled Channels (CC) calculations have been performed using M3Y+repulsion and Woods-Saxon potentials, where the lowlying 2+ and 3- excitations have been included. A weak imaginary potential was found to be necessary to reproduce the low energy 28Si+28Si data. This probably simulates the effect of the oblate deformation of this nucleus. On the contrary, 30Si is a spherical nucleus, 30Si+30Si is nicely fit by CC calculations and no imaginary potential is needed. For this system, no maximum shows up for the astrophysical S-factor so that we have no evidence for hindrance, as confirmed by the comparison with CC calculations. The logarithmic derivative of the two symmetric systems highlights their different low energy trend. A difference can also be noted in the two barrier distributions, where the high-energy peak present in 28Si+28Si is not observed for 30Si+30Si, probably due to the weaker couplings in last case.

Oxidation of ZrB2 SiC TaSi2 Materials at Ultra High Temperatures

NASA Technical Reports Server (NTRS)

Opila, E.; Smith, J.; Levine, S.; Lorincz, J.; Reigel, M.

2008-01-01

ZrB2 - 20v% SiC - 20v% TaSi2 was oxidized in stagnant air for ten minute cycles for times up to 100 minutes at 1627 C and 1927 C. The sample oxidized at 1627 C showed oxidation resistance better than that of the standard ZrB2 - 20v% SiC. The sample oxidized at 1927 C, however, showed evidence of liquid phase formation and complex oxidation products. The sample exposed at 1927 C was analyzed in detail by scanning electron microprobe and wavelength dispersive spectroscopy to understand the complex oxidation and melting reactions occurring during exposure. The as hot-pressed material shows the formation of a Zr(Ta)B2 phase in addition to the three phases in the nominal composition already noted. After oxidation, the TaSi2 in the matrix was completely reacted to form Ta(Zr)C. The layered oxidation products included SiO2, ZrO2, Ta2O5, and a complex oxide containing both Zr and Ta. Likely reactions are proposed based on thermodynamic phase stability and phase morphology.

Gamma ray irradiated silicon nanowires: An effective model to investigate defects at the interface of Si/SiOx

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yin, Kui; Zhao, Yi; Liu, Liangbin

2014-01-20

The effect of gamma ray irradiation on silicon nanowires was investigated. Here, an additional defect emerged in the gamma-ray-irradiated silicon nanowires and was confirmed with electron spin resonance spectra. {sup 29}Si nuclear magnetic resonance spectroscopy showed that irradiation doses had influence on the Q{sup 4} unit structure. This phenomenon indicated that the unique core/shell structure of silicon nanowires might contribute to induce metastable defects under gamma ray irradiation, which served as a satisfactory model to investigate defects at the interface of Si/SiOx.

Growth of amorphous and epitaxial ZnSiP 2–Si alloys on Si

DOE PAGES

Martinez, Aaron D.; Miller, Elisa M.; Norman, Andrew G.; ...

2018-01-30

ZnSiP 2is a wide band gap material lattice matched with Si, with potential for Si-based optoelectronics. Here, amorphous ZnSiP 2–Si alloys are grown with tunable composition. Films with Si-rich compositions can be crystallized into epitaxial films.

Cold spraying SiC/Al metal matrix composites: effects of SiC contents and heat treatment on microstructure, thermophysical and flexural properties

NASA Astrophysics Data System (ADS)

Gyansah, L.; Tariq, N. H.; Tang, J. R.; Qiu, X.; Feng, B.; Huang, J.; Du, H.; Wang, J. Q.; Xiong, T. Y.

2018-02-01

In this paper, cold spray was used as an additive manufacturing method to fabricate 5 mm thick SiC/Al metal matrix composites with various SiC contents. The effects of SiC contents and heat treatment on the microstructure, thermophysical and flexural properties were investigated. Additionally, the composites were characterized for retention of SiC particulates, splat size, surface roughness and the progressive understanding of strengthening, toughening and cracking mechanisms. Mechanical properties were investigated via three-point bending test, thermophysical analysis, and hardness test. In the as-sprayed state, flexural strength increased from 95.3 MPa to 133.5 MPa, an appreciation of 40% as the SiC contents increased, and the main toughening and strengthening mechanisms were zigzag crack propagation and high retention of SiC particulates respectively. In the heat treatment conditions, flexural strength appreciated significantly compared to the as-sprayed condition and this was as a result of coarsening of pure Al splat. Crack branching, crack deflection and interface delamination were considered as the main toughening mechanisms at the heat treatment conditions. Experimental results were consistent with the measured CTE, hardness, porosity and flexural modulus.

Interdiffusion in U 3Si-Al, U 3Si 2-Al, and USi-Al dispersion fuels during irradiation

NASA Astrophysics Data System (ADS)

Kim, Yeon Soo; Hofman, Gerard L.

2011-03-01

Uranium-silicide compound fuel dispersion in an Al matrix is used in research and test reactors worldwide. Interaction layer (IL) growth between fuel particles and the matrix is one of performance issues. The interaction layer growth data for U 3Si, U 3Si 2 and USi dispersions in Al were obtained from both out-of-pile and in-pile tests. The IL is dominantly U(AlSi) 3 from out-of-pile tests, but its (Al + Si)/U ratio from in-pile tests is higher than the out-of-pile data, because of amorphous behavior of the ILs. IL growth correlations were developed for U 3Si-Al and U 3Si 2-Al. The IL growth rates were dependent on the U/Si ratio of the fuel compounds. During irradiation, however, the IL growth rates did not decrease with the decreasing U/Si ratio by fission. It is reasoned that transition metal fission products in the IL compensate the loss of U atoms by providing chemical potential for Al diffusion and volume expansion by solid swelling and gas bubble swelling. The addition of Mo in U 3Si 2 reduces the IL growth rate, which is similar to that of UMo alloy dispersion in a silicon-added Al matrix.

A multilayered approach of Si/SiO to promote carrier transport in electroluminescence of Si nanocrystals

PubMed Central

2012-01-01

The electroluminescence (EL) and photoluminescence of Si nanocrystals (Si-nc) from multilayered samples of Si/SiO are investigated. Si-nc are formed within Si and SiO layers after furnace annealing. It is found that the presence of Si interlayers creates extra carrier paths for EL emission. A comparative study is further performed on a multilayered Si/SiO sample and a single-layered one with Si and SiO homogeneously mixed. Both samples have the same ratio of Si to O and the same contents of Si and O. The multilayered sample is found to have higher EL intensity, less turn-on voltage, lower resistance, and higher current efficiency than the single-layered one. The results indicate that Si interlayers in Si/SiO may act as carrier channels, which promote carrier transport and enhance the EL emission of Si-nc. PMID:22448989

J-type Carbon Stars: A Dominant Source of 14 N-rich Presolar SiC Grains of Type AB

DOE PAGES

Liu, Nan; Stephan, Thomas; Boehnke, Patrick; ...

2017-07-21

Here, we report Mo isotopic data of 27 new presolar SiC grains, including 12 14N-rich AB ( 14N/ 15N > 440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS grains, which came from low-mass asymptotic giant branch (AGB) stars with large s-process isotope enhancements, with the AB2 grain data demonstrates that AB2 grains show near-solar isotopic compositions and lack s-process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of AB2 grains clearly exclude born-again AGB stars, where the intermediate neutron-capture process (i-process) takesmore » place, as their stellar source. On the other hand, low-mass CO novae and early R- and J-type carbon stars show 13C and 14N excesses but no s-process enhancements and are thus potential stellar sources of AB2 grains. And because both early R-type carbon stars and CO novae are rare objects, the abundant J-type carbon stars (10%–15% of all carbon stars) are thus likely to be a dominant source of AB2 grains.« less

J-type Carbon Stars: A Dominant Source of 14 N-rich Presolar SiC Grains of Type AB

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Nan; Stephan, Thomas; Boehnke, Patrick

Here, we report Mo isotopic data of 27 new presolar SiC grains, including 12 14N-rich AB ( 14N/ 15N > 440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS grains, which came from low-mass asymptotic giant branch (AGB) stars with large s-process isotope enhancements, with the AB2 grain data demonstrates that AB2 grains show near-solar isotopic compositions and lack s-process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of AB2 grains clearly exclude born-again AGB stars, where the intermediate neutron-capture process (i-process) takesmore » place, as their stellar source. On the other hand, low-mass CO novae and early R- and J-type carbon stars show 13C and 14N excesses but no s-process enhancements and are thus potential stellar sources of AB2 grains. And because both early R-type carbon stars and CO novae are rare objects, the abundant J-type carbon stars (10%–15% of all carbon stars) are thus likely to be a dominant source of AB2 grains.« less

Design and simulation of betavoltaic angle sensor Based on ⁶³Ni-Si.

PubMed

Ghasemi Nejad, Gholam Reza; Rahmani, Faezeh

2016-01-01

A theoretical design and simulation of betavoltaic angle sensor (beta-AS) based on (63)Ni-Si using MCNP code is presented in this article. It can measure the full angle of 0-360° in the temperature range of 233-353 K. Beta-AS is composed of semicircular (63)Ni as the beta source, which rotates along the circular (four-quadrant) surface of Si as a semiconductor (in p-n structure), so that the change in the source angle in relation to Si surface can be measured based on the changes in V(oc) observed in each quadrant of Si. For better performance, characteristics of Si and (63)Ni have been optimized: N(D) and N(A) values of 8e19 and 4e18 cm(-3) (donor and acceptor doping concentration in Si, respectively), source thickness and activity of 1.5 µm and 18 mCi, respectively. The relation between angle and V(oc) is also investigated. The maximum difference between measured and real values of angle (the worst case, i.e., 0.18° for the angle of 45°) occurs at 233 K. It has been shown that sensitivity of the sensor decreases with an increase of angle. The results also show that the change in activity does not affect the sensitivity. Copyright © 2015 Elsevier Ltd. All rights reserved.

Ab initio chemical kinetics for SiH3 reactions with Si(x)H2x+2 (x = 1-4).

PubMed

Raghunath, P; Lin, M C

2010-12-30

Gas-phase kinetics and mechanisms of SiH(3) reactions with SiH(4), Si(2)H(6), Si(3)H(8), and Si(4)H(10), processes of relevance to a-Si thin-film deposition, have been investigated by ab initio molecular orbital and transition-state theory (TST) calculations. Geometric parameters of all the species involved in the title reactions were optimized by density functional theory at the B3LYP and BH&HLYP levels with the 6-311++G(3df,2p) basis set. The potential energy surface of each reaction was refined at the CCSD(T)/6-311++G(3df,2p) level of theory. The results show that the most favorable low energy pathways in the SiH(3) reactions with these silanes occur by H abstraction, leading to the formation of SiH(4) + Si(x)H(2x+1) (silanyl) radicals. For both Si(3)H(8) and n-Si(4)H(10) reactions, the lowest energy barrier channels take place by secondary Si-H abstraction, yielding SiH(4) + s-Si(3)H(7) and SiH(4) + s-Si(4)H(9), respectively. In the i-Si(4)H(10) reaction, tertiary Si-H abstraction has the lowest barrier producing SiH(4) + t-Si(4)H(9). In addition, direct SiH(3)-for-X substitution reactions forming Si(2)H(6) + X (X = H or silanyls) can also occur, but with significantly higher reaction barriers. A comparison of the SiH(3) reactions with the analogous CH(3) reactions with alkanes has been made. The rate constants for low-energy product channels have been calculated for the temperature range 300-2500 K by TST with Eckart tunneling corrections. These results, together with predicted heats of formation of various silanyl radicals and Si(4)H(10) isomers, have been tabulated for modeling of a-Si:H film growth by chemical vapor deposition.

Effect of AlB2 on the P-threshold in Al-Si alloy

NASA Astrophysics Data System (ADS)

Wu, Yuying; Liu, Xiangfa

2018-06-01

The nucleation of primary Si in Al-Si alloys has been investigated in this work. It was found that there was a threshold concentration of P, below which AlP can not heterogeneous nucleate primary Si in Al-12 wt%Si alloy. AlB2 can not nucleate primary Si directly, but the presence of AlB2 may assist the nucleation of AlP leading to the nucleation of primary Si particles. In addition, with addition of AlB2, the nucleation efficiency of AlP can be improved in Al-18 wt%Si alloy. The orientation relationship between AlB2 and AlP has been calculated, and the adsorption model for AlB2 and AlP was proposed in this work.

Coherent Phonon Transport Measurement and Controlled Acoustic Excitations Using Tunable Acoustic Phonon Source in GHz-sub THz Range with Variable Bandwidth.

PubMed

Shen, Xiaohan; Lu, Zonghuan; Timalsina, Yukta P; Lu, Toh-Ming; Washington, Morris; Yamaguchi, Masashi

2018-05-04

We experimentally demonstrated a narrowband acoustic phonon source with simultaneous tunabilities of the centre frequency and the spectral bandwidth in the GHz-sub THz frequency range based on photoacoustic excitation using intensity-modulated optical pulses. The centre frequency and bandwidth are tunable from 65 to 381 GHz and 17 to 73 GHz, respectively. The dispersion of the sound velocity and the attenuation of acoustic phonons in silicon dioxide (SiO 2 ) and indium tin oxide (ITO) thin films were investigated using the acoustic phonon source. The sound velocities of SiO 2 and ITO films were frequency-independent in the measured frequency range. On the other hand, the phonon attenuations of both of SiO 2 and ITO films showed quadratic frequency dependences, and polycrystalline ITO showed several times larger attenuation than those in amorphous SiO 2 . In addition, the selective excitation of mechanical resonance modes was demonstrated in nanoscale tungsten (W) film using acoustic pulses with various centre frequencies and spectral widths.

Strength, toughness and R-curve behaviour of SiC whisker-reinforced composite Si3N4 with reference to monolithic Si3N4

NASA Technical Reports Server (NTRS)

Choi, S. R.; Salem, J. A.

1992-01-01

The flexural strength and fracture toughness of 30 vol pct SiC whisker-reinforced Si3N4 material were determined as a function of temperature from 25 to 1400 C in an air environment. It was found that both strength and toughness of the composite material were almost the same as those of the monolithic counterpart. The room-temperature strength was retained up to 1100 C; however, appreciable strength degradation started at 1200 C and reached a maximum at 1400 C due to stable crack growth. In contrast, the fracture toughness of the two materials was independent of temperature with an average value of 5.66 MPa sq rt m. It was also observed that the composite material exhibited no rising R-curve behavior at room temperature, as was the case for the monolithic material. These results indicate that SiC whisker addition to the Si3N4 matrix did not provide any favorable effects on strength, toughness and R-curve behavior.

Testing contamination source identification methods for water distribution networks

DOE PAGES

Seth, Arpan; Klise, Katherine A.; Siirola, John D.; ...

2016-04-01

In the event of contamination in a water distribution network (WDN), source identification (SI) methods that analyze sensor data can be used to identify the source location(s). Knowledge of the source location and characteristics are important to inform contamination control and cleanup operations. Various SI strategies that have been developed by researchers differ in their underlying assumptions and solution techniques. The following manuscript presents a systematic procedure for testing and evaluating SI methods. The performance of these SI methods is affected by various factors including the size of WDN model, measurement error, modeling error, time and number of contaminant injections,more » and time and number of measurements. This paper includes test cases that vary these factors and evaluates three SI methods on the basis of accuracy and specificity. The tests are used to review and compare these different SI methods, highlighting their strengths in handling various identification scenarios. These SI methods and a testing framework that includes the test cases and analysis tools presented in this paper have been integrated into EPA’s Water Security Toolkit (WST), a suite of software tools to help researchers and others in the water industry evaluate and plan various response strategies in case of a contamination incident. Lastly, a set of recommendations are made for users to consider when working with different categories of SI methods.« less

Fabrication of mullite-bonded porous SiC ceramics from multilayer-coated SiC particles through sol-gel and in-situ polymerization techniques

NASA Astrophysics Data System (ADS)

Ebrahimpour, Omid

In this work, mullite-bonded porous silicon carbide (SiC) ceramics were prepared via a reaction bonding technique with the assistance of a sol-gel technique or in-situ polymerization as well as a combination of these techniques. In a typical procedure, SiC particles were first coated by alumina using calcined powder and alumina sol via a sol-gel technique followed by drying and passing through a screen. Subsequently, they were coated with the desired amount of polyethylene via an in-situ polymerization technique in a slurry phase reactor using a Ziegler-Natta catalyst. Afterward, the coated powders were dried again and passed through a screen before being pressed into a rectangular mold to make a green body. During the heating process, the polyethylene was burnt out to form pores at a temperature of about 500°C. Increasing the temperature above 800°C led to the partial oxidation of SiC particles to silica. At higher temperatures (above 1400°C) derived silica reacted with alumina to form mullite, which bonds SiC particles together. The porous SiC specimens were characterized with various techniques. The first part of the project was devoted to investigating the oxidation of SiC particles using a Thermogravimetric analysis (TGA) apparatus. The effects of particle size (micro and nano) and oxidation temperature (910°C--1010°C) as well as the initial mass of SiC particles in TGA on the oxidation behaviour of SiC powders were evaluated. To illustrate the oxidation rate of SiC in the packed bed state, a new kinetic model, which takes into account all of the diffusion steps (bulk, inter and intra particle diffusion) and surface oxidation rate, was proposed. Furthermore, the oxidation of SiC particles was analyzed by the X-ray Diffraction (XRD) technique. The effect of different alumina sources (calcined Al2O 3, alumina sol or a combination of the two) on the mechanical, physical, and crystalline structure of mullite-bonded porous SiC ceramics was studied in the

Silicon etching using only Oxygen at high temperature: An alternative approach to Si micro-machining on 150 mm Si wafers

NASA Astrophysics Data System (ADS)

Chai, Jessica; Walker, Glenn; Wang, Li; Massoubre, David; Tan, Say Hwa; Chaik, Kien; Hold, Leonie; Iacopi, Alan

2015-12-01

Using a combination of low-pressure oxygen and high temperatures, isotropic and anisotropic silicon (Si) etch rates can be controlled up to ten micron per minute. By varying the process conditions, we show that the vertical-to-lateral etch rate ratio can be controlled from 1:1 isotropic etch to 1.8:1 anisotropic. This simple Si etching technique combines the main respective advantages of both wet and dry Si etching techniques such as fast Si etch rate, stiction-free, and high etch rate uniformity across a wafer. In addition, this alternative O2-based Si etching technique has additional advantages not commonly associated with dry etchants such as avoiding the use of halogens and has no toxic by-products, which improves safety and simplifies waste disposal. Furthermore, this process also exhibits very high selectivity (>1000:1) with conventional hard masks such as silicon carbide, silicon dioxide and silicon nitride, enabling deep Si etching. In these initial studies, etch rates as high as 9.2 μm/min could be achieved at 1150 °C. Empirical estimation for the calculation of the etch rate as a function of the feature size and oxygen flow rate are presented and used as proof of concepts.

Caesium sputter ion source compatible with commercial SIMS instruments

NASA Astrophysics Data System (ADS)

Belykh, S. F.; Palitsin, V. V.; Veryovkin, I. V.; Kovarsky, A. P.; Chang, R. J. H.; Adriaens, A.; Dowsett, M.; Adams, F.

2006-07-01

A simple design for a caesium sputter cluster ion source compatible with commercially available secondary ion mass spectrometers is reported. This source has been tested with the Cameca IMS 4f instrument using the cluster Si n- and Cu n- ions, and will shortly be retrofitted to the floating low energy ion gun (FLIG) of the type used on the Cameca 4500/4550 quadruple instruments. Our experiments with surface characterization and depth profiling conducted to date demonstrate improvements of analytical capabilities of the SIMS instrument due to the non-additive enhancement of secondary ion emission and shorter ion ranges of polyatomic projectiles compared to atomic ions with the same impact energy.

Two Populations of SiO Masers in the Galactic Bulge

NASA Astrophysics Data System (ADS)

Trapp, Adam; Rich, Robert Michael; Morris, Mark; Pihlstrom, Ylva; Sjouwerman, Lorant; Claussen, Mark J.; Stroh, Michael

2017-01-01

We present a summary of the kinematics of stellar SiO masers observed in the direction of the galactic bulge with ALMA (885 sources), and the JVLA (2,479 sources). These objects are selected by color from the MSX point source catalog, which has given an SiO detection rate of ~70%. The presented sample, along with the ~24,000 sources still being observed and reduced, enable radial velocity measurements even in regions with extreme optical extinction. These maser stars are compared to the known bulge surveys: APOGEE (~25,000 sources), BRAVA (~8000 sources), and GIBS (~6,400 sources). We have found that BAaDE stars in the direction of the bulge exist in two subpopulations: (1) A kinematically hot population exhibiting cylindrical rotation consistent with the other bulge surveys, and (2) a kinematically cold population more consistent with a disk population. In the ALMA data, we find evidence for a -200 km/s feature at (l,b) = (-9,0), possibly the symmetric complement to a previously proposed +200 km/s feature (Nidever 2012), that we do not confirm with our data.

The localization and crystallographic dependence of Si suboxide species at the SiO2/Si interface

NASA Technical Reports Server (NTRS)

Grunthaner, P. J.; Hecht, M. H.; Grunthaner, F. J.; Johnson, N. M.

1987-01-01

X-ray photoemission spectroscopy has been used to examine the localization and crystallographic dependence of Si(+), Si(2+), and Si(3+) suboxide states at the SiO2/Si interface for (100)and (111)-oriented substrates with gate oxide quality thermal oxides. The Si(+) and Si(2+) states are localized within 6-10 A of the interface while the Si(3+) state extends about 30 A into the bulk SiO2. The distribution of Si(+) and Si(2+) states shows a strong crystallographic dependence with Si(2+) dominating on (100) substrates and Si(+) dominating on (111) substrates. This crystallographic dependence is anticipated from consideration of ideal unreconstructed (100) and (111) Si surfaces, suggesting that (1) the Si(+) and Si(2+) states are localized immediately within the first monolayer at the interface and (2) the first few monolayers of substrate Si atoms are not significantly displaced from the bulk. The total number of suboxide states observed at the SiO2/Si interface corresponds to 94 and 83 percent of a monolayer for these (100) and (111) substrates, respectively.

Characterization of high-dose and high-energy implanted gate and source diode and analysis of lateral spreading of p gate profile in high voltage SiC static induction transistors

NASA Astrophysics Data System (ADS)

Onose, Hidekatsu; Kobayashi, Yutaka; Onuki, Jin

2017-03-01

The effect of the p gate dose on the characteristics of the gate-source diode in SiC static induction transistors (SIT) was investigated. It was found that a dose of 1.5 × 1014 cm-2 yields a pn junction breakdown voltage higher than 60 V and good forward characteristics. A normally on SiC SIT was fabricated and demonstrated. A blocking voltage higher than 2.0 kV at a gate-source voltage of -50 V and on-resistance of 70 mΩ cm2 were obtained. Device simulations were performed to investigate the effect of the lateral spreading. By comparing the measured I-V curves with simulation results, the lateral spreading factor was estimated to be about 0.5. The lateral spreading detrimentally affected the electrical properties of the SIT made using implantations at energies higher than 1 MeV.

Microstructural characteristics and aging response of Zn-containing Al-Mg-Si-Cu alloy

NASA Astrophysics Data System (ADS)

Cai, Yuan-hua; Wang, Cong; Zhang, Ji-shan

2013-07-01

Al-Mg-Si-Cu alloys with and without Zn addition were fabricated by conventional ingot metallurgy method. The microstructures and properties were investigated using optical microscopy (OM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), tensile test, hardness test, and electrical conductivity measurement. It is found that the as-cast Al-Mg-Si-Cu-Zn alloy is composed of coarse dendritic grains, long needle-like β/δ-AlFeSi white intermetallics, and Chinese script-like α-AlFeSi compounds. During high temperature homogenization treatment, only harmful needle-like β-AlFeSi phase undergoes fragmentation and spheroidizing at its tips, and the destructive needle-like δ-phase does not show any morphological and size changes. Phase transitions from β-AlFeSi to α-AlFeSi and from δ-AlFeSi to β-AlFeSi are also not found. Zn addition improves the aging hardening response during the former aging stage and postpones the peak-aged hardness to a long aging time. In T4 condition, Zn addition does not obviously increase the yield strength and decrease the elongation, but it markedly improves paint-bake hardening response during paint-bake cycle. The addition of 0.5wt% Zn can lead to an increment of 99 MPa in yield strength compared with the value of 69 MPa for the alloy without Zn after paint-bake cycle.

A comparative study of Si-containing electrolyte additives for lithium ion battery: Which one is better and why is it better

NASA Astrophysics Data System (ADS)

Wang, Kang; Xing, Lidan; Zhu, Yunmin; Zheng, Xiongwen; Cai, Dandan; Li, Weishan

2017-02-01

Influence of two Si-containing electrolyte additives, tris(trimethylsilyl)borate (TMSB) and tris(trimethylsilyl)phosphate (TMSP), on the cyclic stability of high voltage LiNi0.5Mn1.5O4 electrode has been systematically studied in this work. The capacity retention of LiNi0.5Mn1.5O4 cycling in STD (1M LiPF6/EC: EMC = 3:7), TMSB- and TMSP-containing electrolytes is 23%, 85% and 71% after 600 cycles at 1C rate, respectively, revealing that the ability of TMSB on improving the cyclic performance of LiNi0.5Mn1.5O4 is superior to that of TMSP. Experimental and theoretical characterizations show that the preferential reaction of both TMSB and TMSP generates thin and uniform film on LiNi0.5Mn1.5O4 surface, which effectively suppress the continuous oxidation reaction of electrolyte. While the film generated from TMSB, which contains B and Si-rich compounds, shows better ability on restraining the growth of interfacial resistance during cycling, resulting in better cyclic stability of LiNi0.5Mn1.5O4 than that of TMSP.

Hydroxychloroquine-conjugated gold nanoparticles for improved siRNA activity.

PubMed

Perche, F; Yi, Y; Hespel, L; Mi, P; Dirisala, A; Cabral, H; Miyata, K; Kataoka, K

2016-06-01

Current technology of siRNA delivery relies on pharmaceutical dosage forms to route maximal doses of siRNA to the tumor. However, this rationale does not address intracellular bottlenecks governing silencing activity. Here, we tested the impact of hydroxychloroquine conjugation on the intracellular fate and silencing activity of siRNA conjugated PEGylated gold nanoparticles. Addition of hydroxychloroquine improved endosomal escape and increased siRNA guide strand distribution to the RNA induced silencing complex (RISC), both crucial obstacles to the potency of siRNA. This modification significantly improved gene downregulation in cellulo. Altogether, our data suggest the benefit of this modification for the design of improved siRNA delivery systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

Microstructure and Mechanical Property of SiCf/SiC and Cf/SiC Composites

NASA Astrophysics Data System (ADS)

Lee, S. P.; Cho, K. S.; Lee, H. U.; Lee, J. K.; Bae, D. S.; Byun, J. H.

2011-10-01

The mechanical properties of SiC based composites reinforced with different types of fabrics have been investigated, in conjunction with the detailed analyses of their microstructures. The thermal shock properties of SiCf/SiC composites were also examined. All composites showed a dense morphology in the matrix region. Carbon coated PW-SiCf/SiC composites had a good fracture energy, even if their strength was lower than that of PW-Cf/SiC composites. SiCf/SiC composites represented a great reduction of flexural strength at the thermal shock temperature difference of 300 °C.

Effects of TiO2 addition on microwave dielectric properties of Li2MgSiO4 ceramics

NASA Astrophysics Data System (ADS)

Rose, Aleena; Masin, B.; Sreemoolanadhan, H.; Ashok, K.; Vijayakumar, T.

2018-03-01

Silicates have been widely studied for substrate applications in microwave integrated circuits owing to their low dielectric constant and low tangent loss values. Li2MgSiO4 (LMS) ceramics are synthesized through solid-state reaction route using TiO2 as an additive to the pure ceramics. Variations in dielectric properties of LMS upon TiO2 addition in different weight percentages (0.5, 1.5, 2) are studied by keeping the sintering parameters constant. Crystalline structure, phase composition, and microstructure of LMS and LMS-TiO2 ceramics were studied using x-ray diffraction spectrometer and High Resolution Scanning electron microscope. Density was measured through Archimedes method and the microwave dielectric properties were examined by Cavity perturbation technique. LMS achieved relative permittivity (ε r) of 5.73 and dielectric loss (tan δ) of 5.897 × 10‑4 at 8 GHz. In LMS-TiO2 ceramics, 0.5 wt% TiO2 added LMS showed comparatively better dielectric properties than other weight percentages where ε r = 5.67, tan δ = 7.737 × 10‑4 at 8 GHz.

Kapitza resistance of Si/SiO2 interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bowen Deng; Aleksandr Chenatynskiy; Marat Khafizov

2014-02-01

A phonon wave packet dynamics method is used to characterize the Kapitza resistance of a Si/SiO2 interface in a Si/SiO2/Si heterostructure. By varying the thickness of SiO2 layer sandwiched between two Si layers, we determine the Kapitza resistance for the Si/SiO2 interface from both wave packet dynamics and a direct, non-equilibrium molecular dynamics approach. The good agreement between the two methods indicates that they have each captured the anharmonic phonon scatterings at the interface. Moreover, detailed analysis provides insights as to how individual phonon mode scatters at the interface and their contribution to the Kapitza resistance.

MoSi2-Base Hybrid Composites from Aeroengine Applications

NASA Technical Reports Server (NTRS)

Hebsur, Mohan G.

2000-01-01

Addition of about 30 to 50 vol % of Si3N4 particulate to MoSi2 improved low temperature accelerated oxidation resistance by forming a Si2ON2 protective scale and thereby eliminated catastrophic 'pest failure'. The Si3N4 addition also improved the high temperature creep strength by nearly five orders of magnitude, doubled the room temperature toughness, and significantly lowered the CTE of the MoSi2 which eliminated matrix cracking in SCS-6 reinforced composites even after thermal cycling. The SCS-6 fiber reinforcement improved the room temperature fracture toughness by seven times and impact resistance by five times. The composite exhibited this excellent strength and toughness improvement up to 1673 K. More recently, tape casting was adopted as the preferred processing of MoSi2-base composites due to improved fiber spacing, ability to use small diameter fibers, and for lower cost. Good strength and toughness values were also obtained with fine diameter Hi-Nicalon tow fibers. These hybrid composites remain competitive with ceramic matrix composites as a replacement for Ni-base superalloys in aircraft engine applications.

p-BaSi2/n-Si heterojunction solar cells on Si(001) with conversion efficiency approaching 10%: comparison with Si(111)

NASA Astrophysics Data System (ADS)

Deng, Tianguo; Sato, Takuma; Xu, Zhihao; Takabe, Ryota; Yachi, Suguru; Yamashita, Yudai; Toko, Kaoru; Suemasu, Takashi

2018-06-01

B-doped p-BaSi2 epitaxial layers with a hole concentration of 1.1 × 1018 cm‑3 were grown on n-Si(001) using molecular beam epitaxy to fabricate p-BaSi2/n-Si solar cells. The thickness (d) of the p-BaSi2 layer was varied from 20 to 60 nm to investigate its effect on the solar cell performance. The conversion efficiency under an AM1.5 illumination increased with d reaching a maximum of 9.8% at d = 40 nm, which is nearly equal to the highest efficiency (9.9%) for p-BaSi2/n-Si solar cells on Si(111). This study indicated that Si(001) substrates are promising for use in BaSi2 solar cells.

Superlattice Multinanolayered Thin Films of SiO2/SiO2 + Ge for Thermoelectric Device Applications

DTIC Science & Technology

2013-04-05

radioiso- tope sources in the past. In a space nuclear reactor system, the energy source is the heat generated by the controlled fission of uranium ...to the nanodots and/or nanocluster formations in the multilayered thin films. This is one of the expected results of the ion beam bombardments on...very large (150 W m 1 K 1 for Si and 63 W m 1 K 1 for Ge). The lattice thermal conductivity can be substantially reduced by alloy formation between

The role of SiGe buffer in growth and relaxation of Ge on free-standing Si(001) nano-pillars.

PubMed

Zaumseil, P; Kozlowski, G; Schubert, M A; Yamamoto, Y; Bauer, J; Schülli, T U; Tillack, B; Schroeder, T

2012-09-07

We study the growth and relaxation processes of Ge nano-clusters selectively grown by chemical vapor deposition on free-standing 90 nm wide Si(001) nano-pillars with a thin Si(0.23)Ge(0.77) buffer layer. We found that the dome-shaped SiGe layer with a height of about 28 nm as well as the Ge dot deposited on top of it partially relaxes, mainly by elastic lattice bending. The Si nano-pillar shows a clear compliance behavior-an elastic response of the substrate on the growing film-with the tensile strained top part of the pillar. Additional annealing at 800 °C leads to the generation of misfit dislocation and reduces the compliance effect significantly. This example demonstrates that despite the compressive strain generated due to the surrounding SiO(2) growth mask it is possible to realize an overall tensile strain in the Si nano-pillar and following a compliant substrate effect by using a SiGe buffer layer. We further show that the SiGe buffer is able to improve the structural quality of the Ge nano-dot.

HUMAN HEALTH DAMAGES FROM MOBILE SOURCE AIR POLLUTION: ADDITIONAL DELPHI DATA ANALYSIS. VOLUME II

EPA Science Inventory

The report contains the results of additional analyses of the data generated by a panel of medical experts for a study of Human Health Damages from Mobile Source Air Pollution (hereafter referred to as HHD) conducted by the California Air Resources Board in 1973-75 for the U.S. E...

Hot corrosion attack and strength degradation of SiC and Si(sub)3N(sub)4

NASA Technical Reports Server (NTRS)

Smialek, James L.; Fox, Dennis S.; Jacobson, Nathan S.

1987-01-01

Thin films of Na2SO4 and Na2CO3 molten salt deposits were used to corrode sintered SiC and Si3N4 at 1000 C. The resulting attack produced pitting and grain boundary etching resulting in strength decreases ranging from 15 to 50 percent. Corrosion pits were the predominant sources of fracture. The degree of strength decrease was found to be roughly correlated with the depth of the pit, as predicted from fracture toughness considerations. Gas evolution and bubble formation were key aspects of pit formation. Many of the observations of furnace exposures held true in a more realistic burner rig test.

Si-Sb-Te materials for phase change memory applications.

PubMed

Rao, Feng; Song, Zhitang; Ren, Kun; Zhou, Xilin; Cheng, Yan; Wu, Liangcai; Liu, Bo

2011-04-08

Si-Sb-Te materials including Te-rich Si₂Sb₂Te₆ and Si(x)Sb₂Te₃ with different Si contents have been systemically studied with the aim of finding the most suitable Si-Sb-Te composition for phase change random access memory (PCRAM) use. Si(x)Sb₂Te₃ shows better thermal stability than Ge₂Sb₂Te₅ or Si₂Sb₂Te₆ in that Si(x)Sb₂Te₃ does not have serious Te separation under high annealing temperature. As Si content increases, the data retention ability of Si(x)Sb₂Te₃ improves. The 10 years retention temperature for Si₃Sb₂Te₃ film is ~393 K, which meets the long-term data storage requirements of automotive electronics. In addition, Si richer Si(x)Sb₂Te₃ films also show improvement on thickness change upon annealing and adhesion on SiO₂ substrate compared to those of Ge₂Sb₂Te₅ or Si₂Sb₂Te₆ films. However, the electrical performance of PCRAM cells based on Si(x)Sb₂Te₃ films with x > 3.5 becomes worse in terms of stable and long-term operations. Si(x)Sb₂Te₃ materials with 3 < x < 3.5 are proved to be suitable for PCRAM use to ensure good overall performance.

Distribution of nitrogen and defects in SiO(x)N(y)/Si structures formed by the thermal nitridation of SiO2/Si

NASA Technical Reports Server (NTRS)

Vasquez, R. P.; Madhukar, A.; Grunthaner, F. J.; Naiman, M. L.

1986-01-01

Previously reported nitrogen distributions in SiO2 films on Si which have been thermally nitrided at 1000 C have been explained by a kinetic model of the nitridation process which rests upon the effects of interfacial strain. A critical test of this kinetic model is the validity of the predictions regarding nitrogen distributions obtained at other nitridation temperatures. In this work, nitrogen distributions determined via X-ray photoelectron spectroscopy are reported for samples nitrided at 800 and 1150 C, and are shown to be consistent with the kinetic model. In addition, the intensity of a fluorine marker is found to correlate with the nitrogen distribution, and is postulated to be related to kinetically generated defects in the dielectric film, consistent with the strain-dependent energy of formation of defects proposed recently to explain electrical data.

Thin-film formation of Si clathrates on Si wafers

NASA Astrophysics Data System (ADS)

Ohashi, Fumitaka; Iwai, Yoshiki; Noguchi, Akihiro; Sugiyama, Tomoya; Hattori, Masashi; Ogura, Takuya; Himeno, Roto; Kume, Tetsuji; Ban, Takayuki; Nonomura, Shuichi

2014-04-01

In this study, we prepared Si clathrate films (Na8Si46 and NaxSi136) using a single-crystalline Si substrate. Highly oriented film growth of Zintl-phase sodium silicide, which is a precursor of Si clathrate, was achieved by exposing Na vapour to Si substrates under an Ar atmosphere. Subsequent heat treatment of the NaSi film at 400 °C (3 h) under vacuum (<10-2 Pa) resulted in a film of Si clathrates having a thickness of several micrometres. Furthermore, this technique enabled the selective growth of Na8Si46 and NaxSi136 using the appropriate crystalline orientation of Si substrates.

Porphyrin conjugated SiC/SiOx nanowires for X-ray-excited photodynamic therapy.

PubMed

Rossi, F; Bedogni, E; Bigi, F; Rimoldi, T; Cristofolini, L; Pinelli, S; Alinovi, R; Negri, M; Dhanabalan, S C; Attolini, G; Fabbri, F; Goldoni, M; Mutti, A; Benecchi, G; Ghetti, C; Iannotta, S; Salviati, G

2015-01-05

The development of innovative nanosystems opens new perspectives for multidisciplinary applications at the frontier between materials science and nanomedicine. Here we present a novel hybrid nanosystem based on cytocompatible inorganic SiC/SiOx core/shell nanowires conjugated via click-chemistry procedures with an organic photosensitizer, a tetracarboxyphenyl porphyrin derivative. We show that this nanosystem is an efficient source of singlet oxygen for cell oxidative stress when irradiated with 6 MV X-Rays at low doses (0.4-2 Gy). The in-vitro clonogenic survival assay on lung adenocarcinoma cells shows that 12 days after irradiation at a dose of 2 Gy, the cell population is reduced by about 75% with respect to control cells. These results demonstrate that our approach is very efficient to enhance radiation therapy effects for cancer treatments.

Porphyrin conjugated SiC/SiOx nanowires for X-ray-excited photodynamic therapy

NASA Astrophysics Data System (ADS)

Rossi, F.; Bedogni, E.; Bigi, F.; Rimoldi, T.; Cristofolini, L.; Pinelli, S.; Alinovi, R.; Negri, M.; Dhanabalan, S. C.; Attolini, G.; Fabbri, F.; Goldoni, M.; Mutti, A.; Benecchi, G.; Ghetti, C.; Iannotta, S.; Salviati, G.

2015-01-01

The development of innovative nanosystems opens new perspectives for multidisciplinary applications at the frontier between materials science and nanomedicine. Here we present a novel hybrid nanosystem based on cytocompatible inorganic SiC/SiOx core/shell nanowires conjugated via click-chemistry procedures with an organic photosensitizer, a tetracarboxyphenyl porphyrin derivative. We show that this nanosystem is an efficient source of singlet oxygen for cell oxidative stress when irradiated with 6 MV X-Rays at low doses (0.4-2 Gy). The in-vitro clonogenic survival assay on lung adenocarcinoma cells shows that 12 days after irradiation at a dose of 2 Gy, the cell population is reduced by about 75% with respect to control cells. These results demonstrate that our approach is very efficient to enhance radiation therapy effects for cancer treatments.

High Mobility SiGe/Si n-Type Structures and Field Effect Transistors on Sapphire Substrates

NASA Technical Reports Server (NTRS)

Alterovitz, Samuel A.; Ponchak, George E.; Mueller, Carl H.; Croke, Edward T.

2004-01-01

SiGe/Si n-type modulation doped field effect transistors (MODFETs) fabricated on sapphire substrates have been characterized at microwave frequencies for the first time. The highest measured room temperature electron mobility is 1380 sq cm/V-sec at a carrier density of 1.8 x 10(exp 12)/sq cm for a MODFET structure, and 900 sq cm/V-sec at a carrier density of 1.3 x 10/sq cm for a phosphorus ion implanted sample. A two finger, 2 x 200 micron gate n-MODFET has a peak transconductance of 37 mS/mm at a drain to source voltage of 2.5 V and a transducer gain of 6.4 dB at 1 GHz.

Interface properties of SiOxNy layer on Si prepared by atmospheric-pressure plasma oxidation-nitridation

PubMed Central

2013-01-01

SiOxNy films with a low nitrogen concentration (< 4%) have been prepared on Si substrates at 400°C by atmospheric-pressure plasma oxidation-nitridation process using O2 and N2 as gaseous precursors diluted in He. Interface properties of SiOxNy films have been investigated by analyzing high-frequency and quasistatic capacitance-voltage characteristics of metal-oxide-semiconductor capacitors. It is found that addition of N into the oxide increases both interface state density (Dit) and positive fixed charge density (Qf). After forming gas anneal, Dit decreases largely with decreasing N2/O2 flow ratio from 1 to 0.01 while the change of Qf is insignificant. These results suggest that low N2/O2 flow ratio is a key parameter to achieve a low Dit and relatively high Qf, which is effective for field effect passivation of n-type Si surfaces. PMID:23634872

Formation of spherical-shaped GaN and InN quantum dots on curved SiN/Si surface.

PubMed

Choi, Ilgyu; Lee, Hyunjoong; Lee, Cheul-Ro; Jeong, Kwang-Un; Kim, Jin Soo

2018-08-03

This paper reports the formation of GaN and InN quantum dots (QDs) with symmetric spherical shapes, grown on SiN/Si(111). Spherical QDs are grown by modulating initial growth behavior via gallium and indium droplets functioning as nucleation sites for QDs. Field-emission scanning electron microscope (FE-SEM) images show that GaN and InN QDs are formed on curved SiN/Si(111) instead of on a flat surface similar to balls on a latex mattress. This is considerably different from the structural properties of In(Ga)As QDs grown on GaAs or InP. In addition, considering the shape of the other III-V semiconductor QDs, the QDs in this study are very close to the ideal shape of zero-dimensional nanostructures. Transmission-electron microscope images show the formation of symmetric GaN and InN QDs with a round shape, agreeing well with the FE-SEM results. Compared to other III-V semiconductor QDs, the unique structural properties of Si-based GaN and InN QDs are strongly related to the modulation in the initial nucleation characteristics due to the presence of droplets, the degree of lattice mismatch between GaN or InN and SiN/Si(111), and the melt-back etching phenomenon.

Polysilicon Prepared from SiCl4 by Atmospheric-Pressure Non-Thermal Plasma

NASA Astrophysics Data System (ADS)

Li, Xiaosong; Wang, Nan; Yang, Jinhua; Wang, Younian; Zhu, Aimin

2011-10-01

Non-thermal plasma at atmospheric pressure was explored for the preparation of polysilicon from SiCl4. The power supply sources of positive pulse and alternating current (8 kHz and 100 kHz) were compared for polysilicon preparation. The samples prepared by using the 100 kHz power source were crystalline silicon. The effects of H2 and SiCl4 volume fractions were investigated. The optical emission spectra showed that silicon species played an important role in polysilicon deposition

Fabrication technology of Si face and m face on 4H-SiC (0001) epi-layer based on molten KOH etching

NASA Astrophysics Data System (ADS)

Lin, Wen-kui; Zeng, Chun-hong; Sun, Yu-hua; Zhang, Xuan; Li, Zhe; Yang, Tao-tao; Ju, Tao; Zhang, Bao-shun

2018-02-01

Additional scattering of electrons in the complex MOSFET channel caused by off-cut angle of (0001) 4H-SiC wafer, makes accurate crystal face acquisition much desired. Molten KOH was used to etch the circular grooves on the SiC wafer surface in muffle furnace, and hexagonal grooves with SiC crystal symmetry were obtained. Average etching rates at 500°C along <11-20> and <1-100> direction were about 4.826 um/min and 4.112 um/min, respectively,with a etching anisotropy ratio of 1.18. The m face was obtained by controlling the etching time and Si face was obtained by selfstopping effect. The method we developed in this paper has potential applications in the accurate crystal face acquisition of (0001) 4H-SiC epi-wafer, and the preparation of structures based on 4H-SiC.

Surface roughening of undoped and in situ B-doped SiGe epitaxial layers deposited by using reduced pressure chemical vapor deposition

NASA Astrophysics Data System (ADS)

Kim, Youngmo; Park, Jiwoo; Sohn, Hyunchul

2018-01-01

Si1- x Ge x (:B) epitaxial layers were deposited by using reduced pressure chemical vapor deposition with SiH4, GeH4, and B2H6 source gases, and the dependences of the surface roughness of undoped Si1- x Ge x on the GeH4 flow rate and of Si1- x Ge x :B on the B2H6 flow rate were investigated. The root-mean-square (RMS) roughness value of the undoped Si1- x Ge x at constant thickness increased gradually with increasing Ge composition, resulting from an increase in the amplitude of the wavy surface before defect formation. At higher Ge compositions, the residual strain in Si1- x Ge x significantly decreased through the formation of defects along with an abrupt increase in the RMS roughness. The variation of the surface roughness of Si1- x Ge x :B depended on the boron (B) concentration. At low B concentrations, the RMS roughness of Si1- x Ge x remained constant regardless of Ge composition, which is similar to that of undoped Si1- x Ge x . However, at high B concentrations, the RMS roughness of Si1- x Ge x :B increased greatly due to B islanding. In addition, at very high B concentrations ( 9.9 at%), the RMS roughness of Si1- x Ge x :B decreased due to non-epitaxial growth.

Structure and magnetism in Co/X, Fe/Si, and Fe/(FeSi) multilayers

NASA Astrophysics Data System (ADS)

Franklin, Michael Ray

Previous studies have shown that magnetic behavior in multilayers formed by repeating a bilayer unit comprised of a ferromagnetic layer and a non-magnetic spacer layer can be affected by small structural differences. For example, a macroscopic property such as giant magnetoresistance (GMR) is believed to depend significantly upon interfacial roughness. In this study, several complimentary structural probes were used to carefully characterize the structure of several sputtered multilayer systems-Co/Ag, Co/Cu, Co/Mo, Fe/Si, and Fe//[FeSi/]. X-ray diffraction (XRD) studies were used to examine the long-range structural order of the multilayers perpendicular to the plane of the layers. Transmission electron diffraction (TED) studies were used to probe the long-range order parallel to the layer plane. X-ray Absorption Fine Structure (XAFS) studies were used to determine the average local structural environment of the ferromagnetic atoms. For the Co/X systems, a simple correlation between crystal structure and saturation magnetization is discovered for the Co/Mo system. For the Fe/X systems, direct evidence of an Fe-silicide is found for the /[FeSi/] spacer layer but not for the Si spacer layer. Additionally, differences were observed in the magnetic behavior between the Fe in the nominally pure Fe layer and the Fe contained in the /[FeSi/] spacer layers.

Uninterrupted and reusable source for the controlled growth of nanowires

PubMed Central

Sugavaneshwar, R. P.; Nanda, Karuna Kar

2013-01-01

Generally, the length of the oxide nanowires grown by vapor phase transport is limited by the degradation of the source materials. Furthermore, the source material is used once for the nanowires growth. By exploiting the Si-Zn phase diagram, we have developed a simple methodology for the non-catalytic growth of ultralong ZnO nanowires in large area with controllable aspect ratio and branched structures. The insolubility of Zn in Si and the use of a Si cap on the Zn source to prevent local source oxidation of Zn (i. e. prevents the degradation of the source) are the keys to grow longer nanowires without limitations. It has been shown that the aspect ratio can be controlled by thermodynamically (temperature) and more importantly by kinetically (vapor flux). One of the interesting findings is that the same source material can be used for several depositions of oxide nanostructured materials. PMID:23412010

Foreign Object Damage Behavior of a SiC/SiC Composite at Ambient and Elevated Temperatures

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.; Pereira, J. Michael; Gyekenyesi, John P.; Choi, Sung R.

2004-01-01

Foreign object damage (FOD) behavior of a gas-turbine grade SiC/SiC ceramic matrix composite (CMC) was determined at 25 and 1316 C, employing impact velocities from 115 to 440 meters per second by 1.59-mm diameter stell-ball projectiles. Two different types of specimen support were used at each temperature: fully supported and partially supported. For a given temperature, the degree of post-impact strength degradation increased with increasing impact velocity, and was greater in a partially supported configuration than in a fully supported one. The elevated-temperature FOD resistance of the composite, particularly under partially supported loading at higher impact velocities greater than or equal to 350 meters per second, was significantly less than the ambient-temperature counterpart, attributed to a weakening effect of the composite. For fully supported loading, frontal contact stress played a major role in generating composite damage; whereas, for partially supported loading, both frontal contact and backside bending stresses were combined sources of damage generation. The SiC/SiC composite was able to survive higher energy impacts without complete structural failure but suffered more strength affecting damage from low energy impacts than AS800 and SN282 silicon nitrides.

Consolidation of silicon nitride without additives. [for gas turbine engine efficiency increase

NASA Technical Reports Server (NTRS)

Sikora, P. F.; Yeh, H. C.

1976-01-01

The use of ceramics for gas turbine engine construction might make it possible to increase engine efficiency by raising operational temperatures to values beyond those which can be tolerated by metallic alloys. The most promising ceramics being investigated in this connection are Si3N4 and SiC. A description is presented of a study which had the objective to produce dense Si3N4. The two most common methods of consolidating Si3N4 currently being used include hot pressing and reaction sintering. The feasibility was explored of producing a sound, dense Si3N4 body without additives by means of conventional gas hot isostatic pressing techniques and an uncommon hydraulic hot isostatic pressing technique. It was found that Si3N4 can be densified without additions to a density which exceeds 95% of the theoretical value

Comparative studies of Ge and Si p-channel metal-oxide-semiconductor field-effect-transistors with HfSiON dielectric and TaN metal gate

NASA Astrophysics Data System (ADS)

Hu, Ai-Bin; Xu, Qiu-Xia

2010-05-01

Ge and Si p-channel metal-oxide-semiconductor field-effect-transistors (p-MOSFETs) with hafnium silicon oxynitride (HfSiON) gate dielectric and tantalum nitride (TaN) metal gate are fabricated. Self-isolated ring-type transistor structures with two masks are employed. W/TaN metal stacks are used as gate electrode and shadow masks of source/drain implantation separately. Capacitance-voltage curve hysteresis of Ge metal-oxide-semiconductor (MOS) capacitors may be caused by charge trapping centres in GeO2 (1 < x < 2). Effective hole mobilities of Ge and Si transistors are extracted by using a channel conductance method. The peak hole mobilities of Si and Ge transistors are 33.4 cm2/(V · s) and 81.0 cm2/(V · s), respectively. Ge transistor has a hole mobility 2.4 times higher than that of Si control sample.

Highly Enhanced H2 Sensing Performance of Few-Layer MoS2/SiO2/Si Heterojunctions by Surface Decoration of Pd Nanoparticles.

PubMed

Hao, Lanzhong; Liu, Yunjie; Du, Yongjun; Chen, Zhaoyang; Han, Zhide; Xu, Zhijie; Zhu, Jun

2017-10-17

A novel few-layer MoS 2 /SiO 2 /Si heterojunction is fabricated via DC magnetron sputtering technique, and Pd nanoparticles are further synthesized on the device surface. The results demonstrate that the fabricated sensor exhibits highly enhanced responses to H 2 at room temperature due to the decoration of Pd nanoparticles. For example, the Pd-decorated MoS 2 /SiO 2 /Si heterojunction shows an excellent response of 9.2 × 10 3 % to H 2 , which is much higher than the values for the Pd/SiO 2 /Si and MoS 2 /SiO 2 /Si heterojunctions. In addition, the H 2 sensing properties of the fabricated heterojunction are dependent largely on the thickness of the Pd-nanoparticle layer and there is an optimized Pd thickness for the device to achieve the best sensing characteristics. Based on the microstructure characterization and electrical measurements, the sensing mechanisms of the Pd-decorated MoS 2 /SiO 2 /Si heterojunction are proposed. These results indicate that the Pd decoration of few-layer MoS 2 /SiO 2 /Si heterojunctions presents an effective strategy for the scalable fabrication of high-performance H 2 sensors.

Deposition of BN interphase coatings from B-trichloroborazine and its effects on the mechanical properties of SiC/SiC composites

NASA Astrophysics Data System (ADS)

Wu, Haitang; Chen, Mingwei; Wei, Xi; Ge, Min; Zhang, Weigang

2010-12-01

Boron nitride thin films were deposited on silicon carbide fibers by chemical vapor deposition at atmospheric pressure from the single source precursor B-trichloroborazine (Cl 3B 3N 3H 3, TCB). The film growth and structure, as a function of deposition temperature, hydrogen gas flow rate, and deposition time, were discussed. The deposition rate reaches a maximum at 1000 °C, then decreases with the increasing of temperature, and the apparent activation energy of the reaction is 127 kJ/mol. Above 1000 °C, gas-phase nucleation determines the deposition process. The deposited BN films were characterized by Raman spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of BN interphase on the mechanical properties of the unidirectional SiC fiber-reinforced SiC matrix (SiC/SiC) composites was also investigated. The results show that the flexural strength of SiC/SiC composites with and without coating is 276 MPa and 70 MPa, respectively, which indicates that BN interphase coating deposited from B-trichloroborazine precursor can effectively adjust the fiber/matrix interface, thus causing a dramatic increase in the mechanical properties of the composites.

Quantitative investigation into the source of current slump in AlGaN/GaN HEMT on both Si (111) and sapphire: Self-heating and trapping

NASA Astrophysics Data System (ADS)

Bag, Ankush; Mukhopadhyay, Partha; Ghosh, Saptarsi; Das, Palash; Chakraborty, Apurba; Dinara, Syed M.; Kabi, Sanjib; Biswas, Dhurbes

2015-05-01

We have experimentally studied trapping and self-heating effect in terms of current slump in AlGaN/GaN HEMT grown and identically processed on Silicon (111) and Sapphire (0001) substrates. Different responses have been observed through DC characterization of different duty cycle (100%, 50%, 5% and 0.5%) of pulses at drain end. Effect of self-heating is more in case of HEMT on Sapphire due to its comparative poor thermal conductivity whereas trapped charges have strong contribution in current drop of HEMT on Si (111) due to larger lattice as well as thermal expansion coefficient mismatched epitaxy between GaN and Si (111). These results have been compared among substrates that lead us to find out optimal source of current slump quantitatively between traps and self-heating.

Design of High Performance Si/SiGe Heterojunction Tunneling FETs with a T-Shaped Gate

NASA Astrophysics Data System (ADS)

Li, Wei; Liu, Hongxia; Wang, Shulong; Chen, Shupeng; Yang, Zhaonian

2017-03-01

In this paper, a new Si/SiGe heterojunction tunneling field-effect transistor with a T-shaped gate (HTG-TFET) is proposed and investigated by Silvaco-Atlas simulation. The two source regions of the HTG-TFET are placed on both sides of the gate to increase the tunneling area. The T-shaped gate is designed to overlap with N+ pockets in both the lateral and vertical directions, which increases the electric field and tunneling rate at the top of tunneling junctions. Moreover, using SiGe in the pocket regions leads to the smaller tunneling distance. Therefore, the proposed HTG-TFET can obtain the higher on-state current. The simulation results show that on-state current of HTG-TFET is increased by one order of magnitude compared with that of the silicon-based counterparts. The average subthreshold swing (SS) of HTG-TFET is 44.64 mV/dec when V g is varied from 0.1 to 0.4 V, and the point SS is 36.59 mV/dec at V g = 0.2 V. Besides, this design cannot bring the sever Miller capacitance for the TFET circuit design. By using the T-shaped gate and SiGe pocket regions, the overall performance of the TFET is optimized.

Design of High Performance Si/SiGe Heterojunction Tunneling FETs with a T-Shaped Gate.

PubMed

Li, Wei; Liu, Hongxia; Wang, Shulong; Chen, Shupeng; Yang, Zhaonian

2017-12-01

In this paper, a new Si/SiGe heterojunction tunneling field-effect transistor with a T-shaped gate (HTG-TFET) is proposed and investigated by Silvaco-Atlas simulation. The two source regions of the HTG-TFET are placed on both sides of the gate to increase the tunneling area. The T-shaped gate is designed to overlap with N + pockets in both the lateral and vertical directions, which increases the electric field and tunneling rate at the top of tunneling junctions. Moreover, using SiGe in the pocket regions leads to the smaller tunneling distance. Therefore, the proposed HTG-TFET can obtain the higher on-state current. The simulation results show that on-state current of HTG-TFET is increased by one order of magnitude compared with that of the silicon-based counterparts. The average subthreshold swing (SS) of HTG-TFET is 44.64 mV/dec when V g is varied from 0.1 to 0.4 V, and the point SS is 36.59 mV/dec at V g  = 0.2 V. Besides, this design cannot bring the sever Miller capacitance for the TFET circuit design. By using the T-shaped gate and SiGe pocket regions, the overall performance of the TFET is optimized.

Formation of nanoporous Si upon self-organized growth of Al and Si nanostructures.

PubMed

Thøgersen, Annett; Jensen, Ingvild J T; Stange, Marit; Kjeldstad, Torunn; Martinez-Martinez, Diego; Løvvik, Ole Martin; Ulyashin, Alexander G; Diplas, Spyros

2018-08-03

Nanostructured materials offer unique electronic and optical properties compared to their bulk counterparts. The challenging part of the synthesis is to create a balance between the control of design, size limitations, up-scalability and contamination. In this work we show that self-organized Al nanowires in amorphous Si can be produced at room temperature by magnetron co-sputtering using two individual targets. Nanoporous Si, containing nanotunnels with dimensions within the quantum confinement regime, were then made by selective etching of Al. The material properties, film growth, and composition of the films were investigated for different compositions. In addition, the reflectance of the etched film has been measured.

J-type Carbon Stars: A Dominant Source of {sup 14}N-rich Presolar SiC Grains of Type AB

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Nan; Nittler, Larry R.; Alexander, Conel M. O’D.

We report Mo isotopic data of 27 new presolar SiC grains, including 12 {sup 14}N-rich AB ({sup 14}N/{sup 15}N > 440, AB2) and 15 mainstream (MS) grains, and their correlated Sr and Ba isotope ratios when available. Direct comparison of the data for the MS grains, which came from low-mass asymptotic giant branch (AGB) stars with large s -process isotope enhancements, with the AB2 grain data demonstrates that AB2 grains show near-solar isotopic compositions and lack s -process enhancements. The near-normal Sr, Mo, and Ba isotopic compositions of AB2 grains clearly exclude born-again AGB stars, where the intermediate neutron-capture processmore » ( i -process) takes place, as their stellar source. On the other hand, low-mass CO novae and early R- and J-type carbon stars show {sup 13}C and {sup 14}N excesses but no s -process enhancements and are thus potential stellar sources of AB2 grains. Because both early R-type carbon stars and CO novae are rare objects, the abundant J-type carbon stars (10%–15% of all carbon stars) are thus likely to be a dominant source of AB2 grains.« less

Fabrication of Si heterojunction solar cells using P-doped Si nanocrystals embedded in SiNx films as emitters

PubMed Central

2013-01-01

Si heterojunction solar cells were fabricated on p-type single-crystal Si (sc-Si) substrates using phosphorus-doped Si nanocrystals (Si-NCs) embedded in SiNx (Si-NCs/SiNx) films as emitters. The Si-NCs were formed by post-annealing of silicon-rich silicon nitride films deposited by electron cyclotron resonance chemical vapor deposition. We investigate the influence of the N/Si ratio in the Si-NCs/SiNx films on their electrical and optical properties, as well as the photovoltaic properties of the fabricated heterojunction devices. Increasing the nitrogen content enhances the optical gap E04 while deteriorating the electrical conductivity of the Si-NCs/SiNx film, leading to an increased short-circuit current density and a decreased fill factor of the heterojunction device. These trends could be interpreted by a bi-phase model which describes the Si-NCs/SiNx film as a mixture of a high-transparency SiNx phase and a low-resistivity Si-NC phase. A preliminary efficiency of 8.6% is achieved for the Si-NCs/sc-Si heterojunction solar cell. PMID:24188725

Effect of Carbon in Fabrication Al-SiC Nanocomposites for Tribological Application

PubMed Central

Hekner, Bartosz; Myalski, Jerzy; Pawlik, Tomasz; Sopicka-Lizer, Małgorzata

2017-01-01

Aluminium-based hybrid composites are a new class of advanced materials with the potential of satisfying the demands in engineering applications. This paper describes the effects of carbon addition on the formation and properties of AMC with SiC nanoparticles reinforcement. The composites were produced via mechanical alloying followed by hot pressing. Three forms of carbon, graphite (GR), multiwalled carbon nanotubes (CNTs), and, for the first time, glassy carbon (GC), were used for the hybrid composites manufacturing and compared with tribological properties of Al-SiC composite without carbon addition. GC and CNTs enhanced formation of Al-SiC composite particles and resulted in a homogeneous distribution of reinforcing particles. On the other hand, GR addition altered mechanochemical alloying and did not lead to a proper distribution of nanoparticulate SiC reinforcement. Hot pressing technique led to the reaction between Al and carbon as well as SiC particles and caused the formation of Al4C3 and γ-Al2O3. The subsistence of carbon particles in the composites altered the predominant wear mechanisms since the wear reduction and the stabilization of the friction coefficient were observed. GC with simultaneous γ-Al2O3 formation in the hybrid Al-SiC(n)-C composites turned out to be the most effective additive in terms of their tribological behaviour. PMID:28773039

Morphological and Wear behaviour of new Al-SiCmicro-SiCnano hybrid nanocomposites fabricated through powder metallurgy

NASA Astrophysics Data System (ADS)

Arif, Sajjad; Tanwir Alam, Md; Aziz, Tariq; Ansari, Akhter H.

2018-04-01

In the present work, aluminium matrix composites reinforced with 10 wt% SiC micro particles along with x% SiC nano particles (x = 0, 1, 3, 5 and 7 wt%) were fabricated through powder metallurgy. The fabricated hybrid composites were characterized by x-ray diffractometer (XRD), scanning electron microscope (SEM), energy dispersive spectrum (EDS) and elemental mapping. The relative density, hardness and wear behaviour of all hybrid nanocomposites were studied. The influence of various control factors like SiC reinforcement, sliding distance (300, 600, 900 and 1200 m) and applied load (20, 30 and 40 N) were explored using pin-on-disc wear apparatus. The uniform distribution of micro and nano SiC particles in aluminium matrix is confirmed by elemental maps. The hardness and wear test results showed that properties of the hybrid composite containing 5 wt% nano SiC was better than other hybrid composites. Additionally, the wear loss of all hybrid nanocomposites increases with increasing sliding distance and applied load. The identification of wear phenomenon were studied through the SEM images of worn surface.

Microstructure and hydrothermal corrosion behavior of NITE-SiC with various sintering additives in LWR coolant environments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parish, Chad M.; Terrani, Kurt A.; Kim, Young -Jin

Nano-infiltration and transient eutectic phase (NITE) sintering was developed for fabrication of nuclear grade SiC composites. We produced monolithic SiC ceramics using NITE sintering, as candidates for accident-tolerant fuels in light-water reactors (LWRs). In this work, we exposed three different NITE chemistries (yttria-alumina [YA], ceria-zirconia-alumina [CZA], and yttria-zirconia-alumina [YZA]) to autoclave conditions simulating LWR coolant loops. The YZA was most corrosion resistant, followed by CZA, with YA being worst. High-resolution elemental analysis using scanning transmission electron microscopy (STEM) X-ray mapping combined with multivariate statistical analysis (MVSA) datamining helped explain the differences in corrosion. YA-NITE lost all Al from the corrodedmore » region and the ytttria reformed into blocky precipitates. The CZA material lost all Al from the corroded area, and the YZA – which suffered the least corrosion –retained some Al in the corroded region. Lastly, the results indicate that the YZA-NITE SiC is most resistant to hydrothermal corrosion in the LWR environment.« less

Nanocrystalline Si pathway induced unipolar resistive switching behavior from annealed Si-rich SiN{sub x}/SiN{sub y} multilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Xiaofan; Ma, Zhongyuan, E-mail: zyma@nju.edu.cn; Yang, Huafeng

2014-09-28

Adding a resistive switching functionality to a silicon microelectronic chip is a new challenge in materials research. Here, we demonstrate that unipolar and electrode-independent resistive switching effects can be realized in the annealed Si-rich SiN{sub x}/SiN{sub y} multilayers with high on/off ratio of 10{sup 9}. High resolution transmission electron microscopy reveals that for the high resistance state broken pathways composed of discrete nanocrystalline silicon (nc-Si) exist in the Si nitride multilayers. While for the low resistance state the discrete nc-Si regions is connected, forming continuous nc-Si pathways. Based on the analysis of the temperature dependent I-V characteristics and HRTEM photos,more » we found that the break-and-bridge evolution of nc-Si pathway is the origin of resistive switching memory behavior. Our findings provide insights into the mechanism of the resistive switching behavior in nc-Si films, opening a way for it to be utilized as a material in Si-based memories.« less

Atomic-scale analysis of deposition and characterization of a-Si:H thin films grown from SiH radical precursor

NASA Astrophysics Data System (ADS)

Sriraman, Saravanapriyan; Aydil, Eray S.; Maroudas, Dimitrios

2002-07-01

Growth of hydrogenated amorphous silicon films (a-Si:H) on an initial H-terminated Si(001)(2 x1) substrate at T=500 K was studied through molecular-dynamics (MD) simulations of repeated impingement of SiH radicals to elucidate the effects of reactive minority species on the structural quality of the deposited films. The important reactions contributing to film growth were identified through detailed visualization of radical-surface interaction trajectories. These reactions include (i) insertion of SiH into Si-Si bonds, (ii) adsorption onto surface dangling bonds, (iii) surface H abstraction by impinging SiH radicals through an Eley-Rideal mechanism, (iv) surface adsorption by penetration into subsurface layers or dissociation leading to interstitial atomic hydrogen, (v) desorption of interstitial hydrogen into the gas phase, (vi) formation of higher surface hydrides through the exchange of hydrogen, and (vii) dangling-bond-mediated dissociation of surface hydrides into monohydrides. The MD simulations of a-Si:H film growth predict an overall surface reaction probability of 95% for the SiH radical that is in good agreement with experimental measurements. Structural and chemical characterization of the deposited films was based on the detailed analysis of evolution of the films' structure, surface morphology and roughness, surface reactivity, and surface composition. The analysis revealed that the deposited films exhibit high dangling bond densities and rough surface morphologies. In addition, the films are abundant in voids and columnar structures that are detrimental to producing device-quality a-Si:H thin films.

Towards better light harvesting capability for DSSC (dye sensitized solar cells) through addition of Au@SiO2 core-shell nanoparticles

NASA Astrophysics Data System (ADS)

Fadhilah, Nur; Alhadi, Emha Riyadhul Jinan; Risanti, Doty Dewi

2018-04-01

The Au nanoparticles as core can increase the light harvesting due to the strong near-field effect LSPR (Localized Surface Plasmon Resonance), effectively minimized the electron recombination process and also can improve the optical absorption of the dye sensitized. Au@SiO2 core-shell nanoparticles were prepared using SiO2 extracted from Sidoarjo mud volcano. In this work investigated the influence of pH solution and silica shell volume fraction in Au@SiO2 nanoparticles core-shell structure on DSSC loaded with Ru-based dye. From XRD characterization it was found that core-shell contains SiO2, Au, γAl2O3 and traces NaCl. UV-Vis absorption spectra of core-shell showed the position of the surface plasmon AuNP band in the range of 500-600 nm. The Au@SiO2 core-shell with volume fraction of 30ml silica has the highest peak absorbance. The enhanced light absorption is primarily attributed to the LSPR effect of the Au core. Our results on incident photon-to-current conversion efficiency indicates that the presence of SiO2 depending on its volume fraction tends to shift to longer wavelength.

Green synthesis of Si-incorporated hydroxyapatite using sodium metasilicate as silicon precursor and in vitro antibiotic release studies.

PubMed

Abinaya Sindu, P; Kolanthai, Elayaraja; Suganthi, R V; Thanigai Arul, K; Manikandan, E; Catalani, Luiz H; Narayana Kalkura, S

2017-10-01

The aim of the current study is to synthesize nanosized silicon incorporated HAp (Si-HAP) using sodium metasilicate as the silicon source. The sol-gel derived samples were further subjected to microwave irradiation. Incorporation of Si into HAp did not alter the HAp phase, as confirmed by the X-ray diffraction analysis (XRD). Moreover, variation in the lattice parameters of the Si-incorporated HAp indicates that Si is substituted into the HAp lattice. The decrease in the intensity of the peaks attributed to hydroxyl groups, which appeared in the FTIR and Raman spectra of Si-HAp, further confirms the Si substitution in HAp lattices. The silicon incorporation enhanced the nanorods length by 70%, when compared to that of pure HAp. Microwave irradiation improved the crystallinity of Si-HAp when compared to as-synthesized Si-HAp samples. As-synthesized Si-incorporated HAp sample showed an intense blue emission under UV excitation. Microwave irradiation reduced the intensity of blue emission and exhibited red shift due to the reduction of defects in the Si-HAp crystal. The morphological change from rod to spherical and ribbon-like forms was observed with an increase in silicon content. Further, Si-HAp exhibited better bioactivity and low dissolution rate. Initially there was a burst release of amoxicillin from all the samples, subsequently it followed a sustained release. The microwave-irradiated HAp showed extended period of sustained release than that of as-synthesized HAp and Si-HAp. Similarly, the microwave-irradiated Si-incorporated samples exhibited prolonged drug release, as compared to that of the as-synthesized samples. Hence, Si-HAp is rapidly synthesized by a simple and cost effective method without inducing any additional phases, as compared to the conventional sintering process. This study provides a new insight into the rapid green synthesis of Si-HAp. Si-HAp could emerge as a promising material for the bone tissue replacement and as a drug delivery system

Designing highly active siRNAs for therapeutic applications.

PubMed

Walton, S Patrick; Wu, Ming; Gredell, Joseph A; Chan, Christina

2010-12-01

The discovery of RNA interference (RNAi) generated considerable interest in developing short interfering RNAs (siRNAs) for understanding basic biology and as the active agents in a new variety of therapeutics. Early studies showed that selecting an active siRNA was not as straightforward as simply picking a sequence on the target mRNA and synthesizing the siRNA complementary to that sequence. As interest in applying RNAi has increased, the methods for identifying active siRNA sequences have evolved from focusing on the simplicity of synthesis and purification, to identifying preferred target sequences and secondary structures, to predicting the thermodynamic stability of the siRNA. As more specific details of the RNAi mechanism have been defined, these have been incorporated into more complex siRNA selection algorithms, increasing the reliability of selecting active siRNAs against a single target. Ultimately, design of the best siRNA therapeutics will require design of the siRNA itself, in addition to design of the vehicle and other components necessary for it to function in vivo. In this minireview, we summarize the evolution of siRNA selection techniques with a particular focus on one issue of current importance to the field, how best to identify those siRNA sequences likely to have high activity. Approaches to designing active siRNAs through chemical and structural modifications will also be highlighted. As the understanding of how to control the activity and specificity of siRNAs improves, the potential utility of siRNAs as human therapeutics will concomitantly grow. © 2010 The Authors Journal compilation © 2010 FEBS.

Reaction mechanisms at 4H-SiC/SiO2 interface during wet SiC oxidation

NASA Astrophysics Data System (ADS)

Akiyama, Toru; Hori, Shinsuke; Nakamura, Kohji; Ito, Tomonori; Kageshima, Hiroyuki; Uematsu, Masashi; Shiraishi, Kenji

2018-04-01

The reaction processes at the interface between SiC with 4H structure (4H-SiC) and SiO2 during wet oxidation are investigated by electronic structure calculations within the density functional theory. Our calculations for 4H-SiC/SiO2 interfaces with various orientations demonstrate characteristic features of the reaction depending on the crystal orientation of SiC: On the Si-face, the H2O molecule is stable in SiO2 and hardly reacts with the SiC substrate, while the O atom of H2O can form Si-O bonds at the C-face interface. Two OH groups are found to be at least necessary for forming new Si-O bonds at the Si-face interface, indicating that the oxidation rate on the Si-face is very low compared with that on the C-face. On the other hand, both the H2O molecule and the OH group are incorporated into the C-face interface, and the energy barrier for OH is similar to that for H2O. By comparing the calculated energy barriers for these reactants with the activation energies of oxide growth rate, we suggest the orientation-dependent rate-limiting processes during wet SiC oxidation.

Brazing SiC/SiC Composites to Metals

NASA Technical Reports Server (NTRS)

Steffier, Wayne S.

2004-01-01

Experiments have shown that active brazing alloys (ABAs) can be used to join SiC/SiC composite materials to metals, with bond strengths sufficient for some structural applications. The SiC/SiC composite coupons used in the experiments were made from polymerbased SiC fiber preforms that were chemical-vapor-infiltrated with SiC to form SiC matrices. Some of the metal coupons used in the experiments were made from 304 stainless steel; others were made from oxygen-free, high-conductivity copper. Three ABAs were chosen for the experiments: two were chosen randomly from among a number of ABAs that were on hand at the time; the third ABA was chosen because its titanium content (1.25 percent) is less than those of the other two ABAs (1.75 and 4.5 percent, respectively) and it was desired to evaluate the effect of reducing the titanium content, as described below. The characteristics of ABAs that are considered to be beneficial for the purpose of joining SiC/SiC to metal include wettability, reactivity, and adhesion to SiC-based ceramics. Prior to further development, it was verified that the three chosen ABAs have these characteristics. For each ABA, suitable vacuum brazing process conditions were established empirically by producing a series of (SiC/SiC)/ABA wetting samples. These samples were then sectioned and subjected to scanning electron microscopy (SEM) and energy-dispersive x-ray spectrometry (EDS) for analysis of their microstructures and compositions. Specimens for destructive mechanical tests were fabricated by brazing of lap joints between SiC/SiC coupons 1/8-in. (.3.2- mm) thick and, variously, stainless steel or copper tabs. The results of destructive mechanical tests and the SEM/EDS analysis were used to guide the development of a viable method of brazing the affected materials.

XAFS studies on a modified Al-Si hypoeutectic alloy

NASA Astrophysics Data System (ADS)

Srirangam, V. S. Prakash; Chattopadhyay, S.; Shibata, T.; Kaduk, J. A.; Miller, J. T.; Segre, C. U.; Shankar, S.

2009-11-01

To understand the role of Sr in doped aluminium-silicon alloys, we have conducted for the first time, Sr- K edge XAFS measurements on Al-3%Si-0.04%Sr. Aluminium-Silicon alloys are widely used in automobile and aerospace applications. Modification of these alloys with addition of trace levels of Sr (200-400 ppm) results in changing the morphology of Si eutectic from "plate" like structure to "fibrous" structure. Several theories have been proposed to understand the mechanism of modification of eutectic phases with Sr addition in these alloys, but there is no conclusive evidence in support of these theories. From our XAFS analysis, we suggest Sr-Si bonds and Sr-Sr correlations may be responsible for the morphological transformation observed in the alloy.

Nanocatalytic growth of Si nanowires from Ni silicate coated SiC nanoparticles on Si solar cell.

PubMed

Parida, Bhaskar; Choi, Jaeho; Ji, Hyung Yong; Park, Seungil; Lim, Gyoungho; Kim, Keunjoo

2013-09-01

We investigated the nanocatalytic growth of Si nanowires on the microtextured surface of crystalline Si solar cell. 3C-SiC nanoparticles have been used as the base for formation of Ni silicate layer in a catalytic reaction with the Si melt under H2 atmosphere at an annealing temperature of 1100 degrees C. The 10-nm thick Ni film was deposited after the SiC nanoparticles were coated on the microtextured surface of the Si solar cell by electron-beam evaporation. SiC nanoparticles form a eutectic alloy surface of Ni silicate and provide the base for Si supersaturation as well as the Ni-Si alloy layer on Si substrate surface. This bottom reaction mode for the solid-liquid-solid growth mechanism using a SiC nanoparticle base provides more stable growth of nanowires than the top reaction mode growth mechanism in the absence of SiC nanoparticles. Thermally excited Ni nanoparticle forms the eutectic alloy and provides collectively excited electrons at the alloy surface, which reduces the activation energy of the nanocatalytic reaction for formation of nanowires.

Oxide Structure Dependence of SiO2/SiOx/3C-SiC/n-Type Si Nonvolatile Resistive Memory on Memory Operation Characteristics

NASA Astrophysics Data System (ADS)

Yamaguchi, Yuichiro; Shouji, Masatsugu; Suda, Yoshiyuki

2012-11-01

We have investigated the dependence of the oxide layer structure of our previously proposed metal/SiO2/SiOx/3C-SiC/n-Si/metal metal-insulator-semiconductor (MIS) resistive memory device on the memory operation characteristics. The current-voltage (I-V) measurement and X-ray photoemission spectroscopy results suggest that SiOx defect states mainly caused by the oxidation of 3C-SiC at temperatures below 1000 °C are related to the hysteresis memory behavior in the I-V curve. By restricting the SiOx interface region, the number of switching cycles and the on/off current ratio are more enhanced. Compared with a memory device formed by one-step or two-step oxidation of 3C-SiC, a memory device formed by one-step oxidation of Si/3C-SiC exhibits a more restrictive SiOx interface with a more definitive SiO2 layer and higher memory performances for both the endurance switching cycle and on/off current ratio.

Formation of Si grains from a NaSi melt prepared by reaction of SiO2 and Na

NASA Astrophysics Data System (ADS)

Yamane, Hisanori; Morito, Haruhiko; Uchikoshi, Masahito

2013-08-01

A mixture of Na2SiO3 and NaSi was found to be formed by reaction of SiO2 and Na at 650 °C as follows: 5Na+3SiO2→2Na2SiO3+NaSi. Single crystals of NaSi were grown by cooling the mixture of Na2SiO3 and NaSi with an excess amount of Na from 850 °C, and polycrystalline Si was obtained by vaporization of Na from the crystals. Coarse grains of Si were also crystallized by Na evaporation after the formation of Na2SiO3 and Si-dissolved liquid Na at 830 °C. The Si grains were collected by washing the product with water. The yield of the Si grains was 85% of the ideal amount expected from the reaction.

Thermal conductivity of hexagonal Si, Ge, and Si1-xGex alloys from first-principles

NASA Astrophysics Data System (ADS)

Gu, Xiaokun; Zhao, C. Y.

2018-05-01

Hexagonal Si and Ge with a lonsdaleite crystal structure are allotropes of silicon and germanium that have recently been synthesized. These materials as well as their alloys are promising candidates for novel applications in optoelectronics. In this paper, we systematically study the phonon transport and thermal conductivity of hexagonal Si, Ge, and their alloys by using the first-principle-based Peierls-Boltzmann transport equation approach. Both three-phonon and four-phonon scatterings are taken into account in the calculations as the phonon scattering mechanisms. The thermal conductivity anisotropy of these materials is identified. While the thermal conductivity parallel to the hexagonal plane for hexagonal Si and Ge is found to be larger than that perpendicular to the hexagonal plane, alloying effectively tunes the thermal conductivity anisotropy by suppressing the thermal conductivity contributions from the middle-frequency phonons. The importance of four-phonon scatterings is assessed by comparing the results with the calculations without including four-phonon scatterings. We find that four-phonon scatterings cannot be ignored in hexagonal Si and Ge as the thermal conductivity would be overestimated by around 10% (40%) at 300 K (900) K. In addition, the phonon mean free path distribution of hexagonal Si, Ge, and their alloys is also discussed.

Verification of Fowler-Nordheim electron tunneling mechanism in Ni/SiO2/n-4H SiC and n+ poly-Si/SiO2/n-4H SiC MOS devices by different models

NASA Astrophysics Data System (ADS)

Kodigala, Subba Ramaiah

2016-11-01

This article emphasizes verification of Fowler-Nordheim electron tunneling mechanism in the Ni/SiO2/n-4H SiC MOS devices by developing three different kinds of models. The standard semiconductor equations are categorically solved to obtain the change in Fermi energy level of semiconductor with effect of temperature and field that extend support to determine sustainable and accurate tunneling current through the oxide layer. The forward and reverse bias currents with variation of electric field are simulated with help of different models developed by us for MOS devices by applying adequate conditions. The latter is quite different from former in terms of tunneling mechanism in the MOS devices. The variation of barrier height with effect of quantum mechanical, temperature, and fields is considered as effective barrier height for the generation of current-field (J-F) curves under forward and reverse biases but quantum mechanical effect is void in the latter. In addition, the J-F curves are also simulated with variation of carrier concentration in the n-type 4H SiC semiconductor of MOS devices and the relation between them is established.