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Sample records for sio2 film induced

  1. SiO2/TiO2 Nanocomposite Films on Polystyrene for Light-Induced Cell Detachment Application.

    PubMed

    Cheng, Zhiguo; Cheng, Kui; Weng, Wenjian

    2017-01-25

    Light-induced cell detachment shows much potential in in vitro cell culture and calls for high-performance light-responsive films. In this study, a smooth and dense SiO2/TiO2 nanocomposite thin film with thickness of around 250 nm was first fabricated on H2O2 treated polystyrene (PS) substrate via a low-temperature sol-gel method. It was observed that the film could well-adhere on the PS surface and the bonding strength became increasingly high with the increase of SiO2 content. The peeling strength and shear strength reached 3.05 and 30.02 MPa, respectively. It was observed the surface of the film could transform into superhydrophilic upon 20 min illumination of ultraviolet with a wavelength of 365 nm (UV365). In cell culture, cells, i.e., NIH3T3 and MC3T3-E1 cells, cultured on SiO2/TiO2 nanocomposite film were easily detached after 10 min of UV365 illumination; the detachment rates reached 90.8% and 88.6%, respectively. Correspondingly, continuous cell sheets with good viability were also easily obtained through the same way. The present work shows that SiO2/TiO2 nanocomposite thin film could be easily prepared on polymeric surface at low temperature. The corresponding film exhibits excellent biocompatibility, high bonding strength, and good light responses. It could be a good candidate for the surface of cell culture utensils with light-induced cell detachment property.

  2. Defect induced phonon scattering for tuning the lattice thermal conductivity of SiO2 thin films

    NASA Astrophysics Data System (ADS)

    Cao, Sen; He, Hu; Zhu, Wenhui

    2017-01-01

    In this work, the thermal properties of nanoscale SiO2 thin films have been systematically investigated with respect to the thickness, crystal orientations and the void defects using non-equilibrium molecular-dynamics (NEMD) simulation. Size effect for the lattice thermal conductivity of nanoscale SiO2 thin films was observed. Additionally, SiO2 thin films with [001] oriented exhibited greater thermal conductivity compared with other crystal orientations which was discussed in terms of phonon density of states (PDOS). Furthermore, the porosity of void defects was introduced to quantify the influence of defects for thermal conductivity. Results exhibited that the thermal conductivity degraded with the increase of porosity. Two thermal conductivity suppression mechanisms, namely, void defects induced material loss interdicting heat conduction and phonon scattering enhanced by the boundary of defects, were proposed. Then, a further simulation was deployed to find that the effect of boundary scattering of defects was dominant in thermal conductivity degradation compared with material loss mechanism. The conclusion suggests that the thermal conductivity could be configured via regulating the distribution of PDOS directly associated with void defects.

  3. Influence of outgassing organic contamination on the transmittance and laser-induced damage of SiO2 sol-gel antireflection film

    NASA Astrophysics Data System (ADS)

    Yang, Liang; Xiang, Xia; Miao, Xinxiang; Li, Zhijie; Zhou, Guorui.; Yan, Zhonghua; Yuan, Xiaodong; Zheng, Wanguo; Zu, Xiaotao

    2015-12-01

    The influence of organic contamination (rubber outgassing) on the transmittance of the SiO2 sol-gel antireflection (AR) film and laser-induced damage threshold (LIDT) at 355 nm for 3ω AR film and at 1064 nm for 1ω AR film is studied. The correlation between the contamination time and the transmittance loss/LIDT of 1ω/3ω AR film is also investigated both in atmospheric and vacuum environments. The results show that the transmittance loss increases with increasing contamination time, and the LIDT decreases with increasing contamination time for both in atmospheric and vacuum environments. In addition, the resistance against contamination of the 1ω film is stronger than 3ω film, and the contamination is more serious in vacuum than in an atmosphere environment for the same contamination time. Meanwhile, the damage mechanism is also discussed. It indicated that both the porous structure and photo-thermal absorption contribute to the decreasing LIDT of the sol-gel AR film.

  4. Hydrogen induced passivation of Si interfaces by Al2O3 films and SiO2/Al2O3 stacks

    NASA Astrophysics Data System (ADS)

    Dingemans, G.; Beyer, W.; van de Sanden, M. C. M.; Kessels, W. M. M.

    2010-10-01

    The role of hydrogen in Si surface passivation is experimentally identified for Al2O3 (capping) films synthesized by atomic layer deposition. By using stacks of SiO2 and deuterated Al2O3, we demonstrate that hydrogen is transported from Al2O3 to the underlying SiO2 already at relatively low annealing temperatures of 400 °C. This leads to a high level of chemical passivation of the interface. Moreover, the thermal stability of the passivation up to 800 °C was significantly improved by applying a thin Al2O3 capping film on the SiO2. The hydrogen released from the Al2O3 film favorably influences the passivation of Si interface defects.

  5. Electron beam induced damage in PECVD Si3N4 and SiO2 films on InP

    NASA Technical Reports Server (NTRS)

    Pantic, Dragan M.; Kapoor, Vik J.; Young, Paul G.; Williams, Wallace D.; Dickman, John E.

    1990-01-01

    Phosphorus rich plasma enhanced chemical vapor deposition (PECVD) of silicon nitride and silicon dioxide films on n-type indium phosphide (InP) substrates were exposed to electron beam irradiation in the 5 to 40 keV range for the purpose of characterizing the damage induced in the dielectic. The electron beam exposure was on the range of 10(exp -7) to 10(exp -3) C/sq cm. The damage to the devices was characterized by capacitance-voltage (C-V) measurements of the metal insulator semiconductor (MIS) capacitors. These results were compared to results obtained for radiation damage of thermal silicon dioxide on silicon (Si) MOS capacitors with similar exposures. The radiation induced damage in the PECVD silicon nitride films on InP was successfully annealed out in an hydrogen/nitrogen (H2/N2) ambient at 400 C for 15 min. The PECVD silicon dioxide films on InP had the least radiation damage, while the thermal silicon dioxide films on Si had the most radiation damage.

  6. Dewetting process of Au films on SiO2 nanowires: Activation energy evaluation

    NASA Astrophysics Data System (ADS)

    Ruffino, F.; Grimaldi, M. G.

    2015-05-01

    SiO2 nanowires gain scientific and technological interest in application fields ranging from nano-electronics, optics and photonics to bio-sensing. Furthermore, the SiO2 nanowires chemical and physical properties, and so their performances in devices, can be enhanced if decorated by metal nanoparticles (such Au) due to local plasmonic effects. In the present paper, we propose a simple, low-cost and high-throughput three-steps methodology for the mass-production of Au nanoparticles coated SiO2 nanowires. It is based on (1) production of the SiO2 nanowires on Si surface by solid state reaction of an Au film with the Si substrate at high temperature; (2) sputtering deposition of Au on the SiO2 nanowires to obtain the nanowires coated by an Au film; and (3) furnace annealing processes to induce the Au film dewetting on the SiO2 nanowires surface. Using scanning electron microscopy analyses, we followed the change of the Au nanoparticles mean versus the annealing time extracting values for the characteristic activation energy of the dewetting process of the Au film on the SiO2 nanowires surface. Such a study can allow the tuning of the nanowires/nanoparticles sizes for desired technological applications.

  7. Superlattice Multinanolayered Thin Films of SiO2/SiO2 + Ge for Thermoelectric Device Applications

    DTIC Science & Technology

    2013-04-05

    the cross-plane ther- mal conductivity values since the more high-energy beam might have destroyed the multinanolayered superlattice thin film...structures. Tasciuc et al. (2000) used the 3v technique to measure the cross-plane ther- mal conductivity of the symmetrically strained Si/Ge superlattices...the two elements (Tritt and Subramanian, 2006). In our superlattice sys- tem, we have prepared the SiO2/SiO2 + Ge amor - phous multilayer films. Our

  8. Impacts of SiO2 planarization on optical thin film properties and laser damage resistance

    NASA Astrophysics Data System (ADS)

    Day, T.; Wang, H.; Jankowska, E.; Reagan, B. A.; Rocca, J. J.; Stolz, C. J.; Mirkarimi, P.; Folta, J.; Roehling, J.; Markosyan, A.; Route, R. R.; Fejer, M. M.; Menoni, C. S.

    2016-12-01

    Lawrence Livermore National Laboratory (LLNL) and Colorado State University (CSU) have co-developed a planarization process to smooth nodular defects. This process consists of individually depositing then etching tens of nanometers of SiO2 with a ratio of 2:1, respectively. Previous work shows incorporating the angular dependent ion surface etching and unidirectional deposition reduces substrate defect cross-sectional area by 90%. This work investigates the micro-structural and optical modifications of planarized SiO2 films deposited by ion beam sputtering (IBS). It is shown the planarized SiO2 thin films have 3x increase in absorption and 18% reduction in thin film stress as compared to control (as deposited) SiO2. Planarized SiO2 films exhibit 13% increase in RMS surface roughness with respect to the control and super polished fused silica substrates. Laser-induced damage threshold (LIDT) results indicate the planarization process has no effect on the onset fluence but alters the shape of the probability vs fluence trace.

  9. Effects of MeV Si ions bombardment on the thermoelectric generator from SiO 2/SiO 2 + Cu and SiO 2/SiO 2 + Au nanolayered multilayer films

    NASA Astrophysics Data System (ADS)

    Budak, S.; Chacha, J.; Smith, C.; Pugh, M.; Colon, T.; Heidary, K.; Johnson, R. B.; Ila, D.

    2011-12-01

    The defects and disorder in the thin films caused by MeV ions bombardment and the grain boundaries of these nanoscale clusters increase phonon scattering and increase the chance of an inelastic interaction and phonon annihilation. We prepared the thermoelectric generator devices from 100 alternating layers of SiO 2/SiO 2 + Cu multi-nano layered superlattice films at the total thickness of 382 nm and 50 alternating layers of SiO 2/SiO 2 + Au multi-nano layered superlattice films at the total thickness of 147 nm using the physical vapor deposition (PVD). Rutherford Backscattering Spectrometry (RBS) and RUMP simulation have been used to determine the stoichiometry of the elements of SiO 2, Cu and Au in the multilayer films and the thickness of the grown multi-layer films. The 5 MeV Si ions bombardments have been performed using the AAMU-Center for Irradiation of Materials (CIM) Pelletron ion beam accelerator to make quantum (nano) dots and/or quantum (quantum) clusters in the multilayered superlattice thin films to decrease the cross plane thermal conductivity, increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric generator devices before and after Si ion bombardments we have measured Seebeck coefficient, cross-plane electrical conductivity, and thermal conductivity in the cross-plane geometry for different fluences.

  10. Laser plasma shockwave cleaning of SiO 2 particles on gold film

    NASA Astrophysics Data System (ADS)

    Ye, Yayun; Yuan, Xiaodong; Xiang, Xia; Dai, Wei; Chen, Meng; Miao, Xinxiang; Lv, Haibing; Wang, Haijun; Zheng, Wanguo

    2011-04-01

    A Nd:YAG laser (1064 nm) induces optical breakdown of the airborne above the gold-coated K9 glass surface and the created shockwave removes the SiO2 particles contaminated on the gold films. The laser cleaning efficiency has been characterized by optical microscopy, dark field imaging, ultraviolet-visible-near infrared spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and the Image-pro software. The relationships between removal ratio and particle position and laser gap distance have been studied in the case of single pulse laser cleaning. The results show that the 1064 nm laser induced plasma shockwave can effectively remove the SiO2 particles. The removal ratio can reach above 90%. The effects of particle position and laser gap distance on the cleaning efficiency are simulated for the single pulse laser cleaning. The simulated results are consistent with the experimental ones.

  11. Effects of thermal annealing on photoluminescence of Si+/C+ implanted SiO2 films

    NASA Astrophysics Data System (ADS)

    Chen, Yin-Yu; Chao, Der-Sheng; Tsai, Hsu-Sheng; Liang, Jenq-Horng

    2016-04-01

    The mechanisms of photoluminescence (PL) originating from Si+/C+ implanted SiO2 are still unclear and need to be clarified. Thus, the purpose of this study is to thoroughly investigate the effects of ion implantation and post-annealing temperature on microstructures and PL characteristics of the Si+/C+ implanted SiO2 films. A comparative analysis was also conducted to clarify the different optical properties between the Si+ and Si+/C+ implanted SiO2 films. In this study, thermally-grown SiO2 films on Si substrates were used as the matrix materials. The Si+ ions and C+ ions were separately implanted into the SiO2 films at room temperature. After ion implantation, the post-annealing treatments were carried out using the furnace annealing (FA) method at various temperatures (600-1100 °C) for 1 h in a N2 ambient. The PL characteristics of the implanted SiO2 films were analyzed using a fluorescence spectrophotometer. The results revealed that the distinct PL peaks were observed at approximately 310, 450 and 650 nm in the Si+-implanted SiO2 films, which can be attributed to the defects, the so-called oxygen deficiency centers (ODCs) and non-bridging oxygen hole centers (NBOHCs), in the materials. In contrast to the Si+ ion implantation, the SiO2 films which were sequentially implanted with Si+ and C+ ions and annealed at 1100 °C can emit white light corresponding to the PL peaks located at around 420, 520 and 720 nm, those can be assigned to the Si-C bonding, C-C graphite-like structure (sp2), and Si nanocrystals, respectively. Moreover, a correlation between the optical properties, microstructures, and bonding configurations of the Si+/C+ implanted SiO2 films was also established in this study.

  12. Thin films of SiO2 and hydroxyapatite on titanium deposited by spray pyrolysis.

    PubMed

    Jokanovic, V; Jokanovic, B; Izvonar, D; Dacic, B

    2008-05-01

    Wet spray pyrolysis of fine, well-dispersed a SiO2 sol was used for the deposition of thin films of silicon dioxide. The sol was obtained by hydrothermal precipitation of silicon acid from a solution at pH = 10. The morphology, roughness, phase composition, chemical homogeneity and the mechanism of the films were investigated by SEM, EDS and IR spectroscopy. The obtained results show a complete covering of the titanium substrate with SiO2 after 3 h of deposition. It was observed that the film thickness increased from 3 to 19 microm, the roughness of the film decreased from 12 to 3 microm, while the morphology of the deposit changed considerably. A hydroxyapatite film was prepared on the so-obtained SiO2 thin film by spray pyrolysis deposition and its morphology and phase composition were investigated.

  13. Highly Luminescent Hybrid SiO2-Coated CdTe Quantum Dots Retained Initial Photoluminescence Efficiency in Sol-Gel SiO2 Film.

    PubMed

    Sun, Hongsheng; Xing, Yugui; Wu, Qinan; Yang, Ping

    2015-02-01

    A highly luminescent silica film was fabricated using tetraethyl orthosilicate (TEOS) and 3-aminopropyltrimethoxysilane (APS) through a controlled sol-gel reaction. The pre-hydrolysis of TEOS and APS which resulted in the mixture of TEOS and APS in a molecular level is a key for the formation of homogenous films. The aminopropyl groups in APS play an important role for obtaining homogeneous film with high photoluminescence (PL). Red-emitting hybrid SiO2-coated CdTe nano-crystals (NCs) were fabricated by a two-step synthesis including a thin SiO2 coating via a sol-gel process and a subsequent refluxing using green-emitting CdTe NCs. The hybrid SiO2-coated CdTe NCs were embedded in a functional SiO2 film via a two-step process including adding the NCs in SiO2 sol with a high viscosity and almost without ethanol and a subsequent spinning coating. The hybrid SiO2-coated CdTe NCs retained their initial PL efficiency (54%) in the film. Being encapsulated with the hybrid NCs in the film, no change on the absorption and PL spectra of red-emitting CdTe NCs (632 nm) was observed. This indicates the hybrid NCs is stable enough during preparation. This phenomenon is ascribed to the controlled sol-gel process and a hybrid SiO2 shell on CdTe NCs. Because these films exhibited high PL efficiency and stability, they will be utilizable for potential applications in many fields.

  14. Thermal conductivity measurement and interface thermal resistance estimation using SiO2 thin film.

    PubMed

    Chien, Heng-Chieh; Yao, Da-Jeng; Huang, Mei-Jiau; Chang, Tien-Yao

    2008-05-01

    In this paper, we describe an easy-to-use method to measure the thermal conductivity of thin films based on an electrical heating/sensing mechanism and a steady-state technique. The method used relative commonly used instruments, and without any signal processing circuit, is easy to be used in such thin-film thermal conductivity measurement. The SiO2 thin-film samples, prepared by thermal oxidation, plasma enhanced chemical vapor deposition (PECVD), and E-beam evaporator, were deposited on a silicon substrate. The apparent thermal conductivity, the intrinsic thermal conductivity of SiO2 films, and the total interface thermal resistance of the heater/SiO2/silicon system were evaluated. Our data showed agreement with those data obtained from previous literatures and from the 3 omega method. Furthermore, by using a sandwiched structure, the interface thermal resistance of Cr/PECVD SiO2 and PECVD SiO2/silicon were also separately evaluated in this work. The data showed that the interface thermal resistance of Cr/PECVD SiO2 (metal/dielectric) is about one order of magnitude larger than that of PECVD SiO2/silicon (dielectric/dielectric).

  15. Nanoporous SiO2 thin films made by atomic layer deposition and atomic etching

    NASA Astrophysics Data System (ADS)

    Ghazaryan, Lilit; Kley, E.-Bernhard; Tünnermann, Andreas; Szeghalmi, Adriana

    2016-06-01

    A new route to prepare nanoporous SiO2 films by mixing atomic-layer-deposited alumina and silica in an Å-scale is presented. The selective removal of Al2O3 from the composites using wet chemical etching with phosphoric acid resulted in nanoporous thin SiO2 layers. A diffusion-controlled dissolution mechanism is identified whereby an interesting reorganization of the residual SiO2 is observed. The atomic scale oxide mixing is decisive in attaining and tailoring the film porosity. The porosity and the refractive index of nanoporous silica films were tailored from 9% to 69% and from 1.40 to 1.13, respectively. The nanoporous silica was successfully employed as antireflection coatings and as diffusion membranes to encapsulate nanostructures.

  16. Nanoporous SiO2 thin films made by atomic layer deposition and atomic etching.

    PubMed

    Ghazaryan, Lilit; Kley, E-Bernhard; Tünnermann, Andreas; Szeghalmi, Adriana

    2016-06-24

    A new route to prepare nanoporous SiO2 films by mixing atomic-layer-deposited alumina and silica in an Å-scale is presented. The selective removal of Al2O3 from the composites using wet chemical etching with phosphoric acid resulted in nanoporous thin SiO2 layers. A diffusion-controlled dissolution mechanism is identified whereby an interesting reorganization of the residual SiO2 is observed. The atomic scale oxide mixing is decisive in attaining and tailoring the film porosity. The porosity and the refractive index of nanoporous silica films were tailored from 9% to 69% and from 1.40 to 1.13, respectively. The nanoporous silica was successfully employed as antireflection coatings and as diffusion membranes to encapsulate nanostructures.

  17. Ion assisted deposition of SiO2 film from silicon

    NASA Astrophysics Data System (ADS)

    Pham, Tuan. H.; Dang, Cu. X.

    2005-09-01

    Silicon dioxide, SiO2, is one of the preferred low index materials for optical thin film technology. It is often deposited by electron beam evaporation source with less porosity and scattering, relatively durable and can have a good laser damage threshold. Beside these advantages the deposition of critical optical thin film stacks with silicon dioxide from an E-gun was severely limited by the stability of the evaporation pattern or angular distribution of the material. The even surface of SiO2 granules in crucible will tend to develop into groove and become deeper with the evaporation process. As the results, angular distribution of the evaporation vapor changes in non-predicted manner. This report presents our experiments to apply Ion Assisted Deposition process to evaporate silicon in a molten liquid form. By choosing appropriate process parameters we can get SiO2 film with good and stable property.

  18. Double-layer antireflection from silver nanoparticle integrated SiO2 layer on silicon wafer: effect of nanoparticle morphology and SiO2 film thickness

    NASA Astrophysics Data System (ADS)

    Parashar, Piyush K.; Sharma, R. P.; Komarala, Vamsi K.

    2017-01-01

    Optical properties of silver nanoparticles (Ag NPs) on SiO2 thin films of variable thickness, as a plasmonic double layer on a plain silicon wafer, are investigated for broadband antireflection. The light confinement into the silicon is found to be sensitive to the SiO2 film thickness of a few nanometers due to an evanescent character of the Ag NPs’ near-fields. The Ag NPs’ size anisotropy plays a pivotal role in incident light coupling due to the sub-wavelength spatial variation of near-fields at the interface, which leads to reflectance spectrum oscillation behavior in the nanoparticles’ surface plasmon resonance and off-resonance regions. With an optimized SiO2/Ag NP double layer, the average reflectance in the 300-1200 nm spectral range is reduced to 14% in comparison to 42% in bare silicon, with a flat minimum reflectance of 3.5% in the 725-1020 nm spectral region. Finite difference time domain calculations are performed for spatial variation of near-fields and their angular distribution of far-fields at different inhomogeneous interfaces (where near-fields exist). The total reflectance from various configurations is simulated theoretically by considering the experimentally optimized physical parameters of the plasmonic double layer to support the observations. To verify the role of SiO2 surface topology apart from the nanoparticle morphology in plasmon near-field coupling, thermally grown SiO2 films are investigated along with the sputtered SiO2 thin films.

  19. The electro-optical behavior of liquid crystal molecules on the surface of SiO2 inorganic thin films.

    PubMed

    Sung, Shi-Joon; Yang, Kee-Jeong; Kim, Dae-Hwan; Do, Yun Seon; Kang, Jin-Kyu; Choi, Byeong-Dae

    2009-12-01

    Inorganic thin films are well known for the liquid crystal alignment layers for LCoS application due to the higher thermal and photochemical stability of inorganic materials. The switching time of liquid crystals is the important factor for the projection application and the faster switching time is required for the high quality display. The switching behavior of liquid crystal molecules on inorganic thin films might be closely related with the surface properties of the inorganic thin films. Therefore the understanding of surface properties of the inorganic thin films is required for the enhancement of the switching time of liquid crystals of LCoS devices. In this work, we prepared the SiO2 inorganic thin films and the electro-optical behavior of liquid crystal molecules on SiO2 thin film was investigated. The sputtering condition of SiO2 thin film was closely related with the thickness and the surface morphology of SiO2 thin film. The switching time of liquid crystals with negative dielectric constant on SiO2 inorganic thin films was dominantly affected by the size of protrusion on the surface of SiO2 thin film and the surface roughness of SiO2 thin film was also related with the switching time of liquid crystals. From these results, it is possible to prepare the SiO2 inorganic thin film suitable for the liquid crystal alignment layer for VAN LC mode.

  20. Anti-fogging nanofibrous SiO(2) and nanostructured SiO(2)-TiO(2) films made by rapid flame deposition and in situ annealing.

    PubMed

    Tricoli, Antonio; Righettoni, Marco; Pratsinis, Sotiris E

    2009-11-03

    Transparent, pure SiO(2), TiO(2), and mixed silica-titania films were (stochastically) deposited directly onto glass substrates by flame spray pyrolysis of organometallic solutions (hexamethyldisiloxane or tetraethyl orthosilicate and/or titanium tetra isopropoxide in xylene) and stabilized by in situ flame annealing. Silicon dioxide films consisted of a network of interwoven nanofibers or nanowires several hundred nm long and 10-15 nm thick, as determined by microscopy. These nanowire or nanofibrous films were formed by chemical vapor deposition (surface growth) on bare glass substrates during scalable combustion of precursor solutions at ambient conditions, for the first time to our knowledge, as determined by thermophoretic sampling of the flame aerosol and microscopy. In contrast, titanium dioxide films consisted of nanoparticles 3-5 nm in diameter that were formed in the flame and deposited onto the glass substrate, resulting in highly porous, lace-like nanostructures. Mixed SiO(2)-TiO(2) films (40 mol % SiO(2)) had similar morphology to pure TiO(2) films. Under normal solar radiation, all such films having a minimal thickness of about 300 nm completely prevented fogging of the glass substrates. These anti-fogging properties were attributed to inhibition of water droplet formation by such super-hydrophilic coatings as determined by wetting angle measurements. Deactivated (without UV radiation) pure TiO(2) coatings lost their super-hydrophilicity and anti-fogging properties even though their wetting angle was reduced by their nanowicking. In contrast, SiO(2)-TiO(2) coatings exhibited the best anti-fogging performance at all conditions taking advantage of the high surface coverage by TiO(2) nanoparticles and the super-hydrophilic properties of SiO(2) on their surface.

  1. Effects of modifiers on the hydrophobicity of SiO2 films from nano-husk ash

    NASA Astrophysics Data System (ADS)

    Xu, Kejing; Sun, Qingwen; Guo, Yanqing; Dong, Shuhua

    2013-07-01

    Nano-husk ashes were prepared by burning rice-husk with self-propagating method. The super-hydrophobic SiO2 films from nano-husk ash were prepared by sol-gel method using hydroxy silicone oil (HSO), hexamethyldisilazane (HMS), or methyl triethoxysilane (MTS) as modifiers. The effects of modifiers on the hydrophobic property of SiO2 films were studied, and the performances were characterized by the XRD, UV-vis, BET, EDS, SEM, IR, and Contact Angle Analyzer. The results showed that the contact angle of SiO2 films was more than 160° when volume ratio of the modifiers to silicon-sodium solution (SSS) was 0.15. The mechanism of modifiers on SiO2 surfaces is a graft copolymerization. The hydrophobic groups in the modifiers replace the hydroxy groups on SiO2 surfaces and make SiO2 surfaces present super-hydrophobicity.

  2. Vapor-phase synthesis of mesoporous SiO2-P2O5 thin films.

    PubMed

    Nishiyama, Norikazu; Kaihara, Junji; Nishiyama, Yuko; Egashira, Yasuyuki; Ueyama, Korekazu

    2007-04-24

    Mesoporous SiO2-P2O5 films were synthesized from the vapor phase onto a silicon substrate. First, a precursor solution of cetyltrimethylammonium bromide (C16TAB), H3PO4, ethanol, and water was deposited on a silicon substrate by a spin-coating method. Then, the C16TAB-H3PO4 composite film was treated with tetraethoxysilane (TEOS) vapor at 90-180 degrees C for 2.5 h. The H3PO4-C16TAB composite formed a hexagonal structure on the silicon substrate before vapor treatment. The TEOS molecules penetrated into the film without a phase transition. The periodic mesostructure of the SiO2-P2O5 films was retained after calcination. The calcined films showed a high proton conductivity of about 0.55 S/cm at room temperature. The molar ratio of P/Si in the SiO2-P2O5 film was as high as 0.43, a level that was not attained by a premixing sol-gel method. The high phosphate group content and the ordered periodic mesostructure contributed to the high proton conductivity.

  3. Optical properties of electrochemically deposited ZnO thin films on colloidal crystal film of SiO2 microspheres.

    PubMed

    Oh, Yong Taeg; Choi, Bum Ho; Shin, Dong Chan

    2012-02-01

    The optical properties of electrochemically deposited ZnO thin films on colloidal crystal film of SiO2 microspheres structures were studied. Colloidal crystal film of SiO2 microspheres were self-assembled by evaporation using SiO2 in solution at a constant 0.1 wt%. ZnO in thin films was then electrochemically deposited on to colloidal crystal film of SiO2 microspheres. During electrochemical deposition, the content of Zn(NO3)2 x 6H2O in solution was 5 wt%, and the process's conditions were varied between of 2-4 V and 30-120 s at room temperature, with subsequent heat-treatment between 200 and 400 degrees C. A smooth surface and uniform thickness of 1.8 microm were obtained at 3 V for 90 s. The highest PL peak intensity was obtained in the ZnO thin film heat-treated at 400 degrees C. The double layered ZnO/SiO2 colloidal crystals showed clearly better emission properties than the SiO2/ZnO and ZnO structures.

  4. The hybrid photocatalyst of TiO2-SiO2 thin film prepared from rice husk silica

    NASA Astrophysics Data System (ADS)

    Klankaw, P.; Chawengkijwanich, C.; Grisdanurak, N.; Chiarakorn, Siriluk

    2012-03-01

    The TiO2-SiO2 thin film was prepared by self-assembly method by mixing SiO2 precursor with titanium precursor solution and aged to obtain a co-precipitation of silica and titanium crystals. Dip coating method was applied for thin film preparation on glass slide. The X-ray diffraction (XRD) of the self-assembly thin film had no characteristic property of SiO2 and even anatase TiO2 but indicated new crystal structure which was determined from the Fourier Transform Infrared Spectrophotometer (FTIR) as a hybridized Ti-O-Si bonding. The surface area and surface volume of the self-assembly sample were increased when SiO2 was incorporated into the film. The self-assembly TiO2-SiO2 thin film exhibited the enhanced photocatalytic decolorization of methylene blue (MB) dye. The advantages of SiO2 are; (1) to increase the adsorbability of the film and (2) to provide the hydroxyl radical to promote the photocatalytic reaction. The self-assembly thin film with the optimum molar ratio (SiO2:TiO2) as 20:80 gave the best performance for photocatalytic decolorization of MB dye with the overall efficiency of 81%.

  5. Direct fabrication of graphene on SiO2 enabled by thin film stress engineering.

    PubMed

    McNerny, Daniel Q; Viswanath, B; Copic, Davor; Laye, Fabrice R; Prohoda, Christophor; Brieland-Shoultz, Anna C; Polsen, Erik S; Dee, Nicholas T; Veerasamy, Vijayen S; Hart, A John

    2014-05-23

    We demonstrate direct production of graphene on SiO2 by CVD growth of graphene at the interface between a Ni film and the SiO2 substrate, followed by dry mechanical delamination of the Ni using adhesive tape. This result is enabled by understanding of the competition between stress evolution and microstructure development upon annealing of the Ni prior to the graphene growth step. When the Ni film remains adherent after graphene growth, the balance between residual stress and adhesion governs the ability to mechanically remove the Ni after the CVD process. In this study the graphene on SiO2 comprises micron-scale domains, ranging from monolayer to multilayer. The graphene has >90% coverage across centimeter-scale dimensions, limited by the size of our CVD chamber. Further engineering of the Ni film microstructure and stress state could enable manufacturing of highly uniform interfacial graphene followed by clean mechanical delamination over practically indefinite dimensions. Moreover, our findings suggest that preferential adhesion can enable production of 2-D materials directly on application-relevant substrates. This is attractive compared to transfer methods, which can cause mechanical damage and leave residues behind.

  6. Accurate characterization of SiO2 thin films using surface acoustic waves.

    PubMed

    Knapp, Matthias; Lomonosov, Alexey M; Warkentin, Paul; Jäger, Philipp M; Ruile, Werner; Kirschner, Hans-Peter; Honal, Matthias; Bleyl, Ingo; Mayer, Andreas P; Reindl, Leonhard M

    2015-04-01

    We have investigated the acoustic properties of silicon dioxide thin films. Therefore, we determined the phase velocity dispersion of LiNbO3 substrate covered with SiO2 deposited by a plasma enhanced chemical vapor deposition and a physical vapor deposition (PVD) process using differential delay lines and laser ultrasonic method. The density p and the elastic constants (c11 and c44) can be extracted by fitting corresponding finite element simulations to the phase velocities within an accuracy of at least +4%. Additionally, we propose two methods to improve the accuracy of the phase velocity determination by dealing with film thickness variation of the PVD process.

  7. Rapid lateral solidification of pure Cu and Au thin films encapsulated in SiO2

    NASA Astrophysics Data System (ADS)

    Kline, J. E.; Leonard, J. P.

    2005-05-01

    Excimer laser melting and lateral resolidification is demonstrated in 200nm thick Cu and Au elemental metal thin films encapsulated between SiO2 layers. Projection irradiation is used to selectively and completely melt lines 3to30μm wide in the metal film—with rapid lateral solidification originating from the unmelted sidewalls of the molten region—resulting in large columnar grains, extending transversely to the middle of the line. Transmission electron microscopy reveals twinning structures and other defects typical of rapid solidification. Encapsulation and control of the fluence are found to be crucial parameters necessary to prevent film dewetting while molten.

  8. Nano-Bi2WO6 functionalized flexible SiO2 fibrous film for water purification

    NASA Astrophysics Data System (ADS)

    Ma, Zhijun; Hu, Zhongliang; He, Xin; Fang, Zaijin; Li, Yang; Qiu, Jianrong

    2016-01-01

    Electrospinning-derived nanofibrous films functionalized by photocatalysts have been extensively studied in the applications of environmental remediation. In this investigation, we propose a simple strategy for preparation of flexible and chemically stable nanofibrous films with high photocatalytic efficiency. Specifically, SiO2 nanofibrous film modified with Bi2WO6 nanoparticles was studied as a representative. Flexible SiO2 nanofibers were derived through sol-gel and electrospinning techniques. By simple soaking in precursor solution of Bi2WO6 and calcination, the SiO2 nanofibrous film was functionalized by Bi2WO6 nanoparticles, forming hierarchically porous composite film. Micro morphology, mechanical property and photocatalytic performance were tuned via changing the concentration of the soaking solution. Photocatalytic removal of organic pollutant from water was performed using RhB (Rhodamine B) as a model. The strategy proposed here is also widely applicable for preparation of composite films modified with other kinds of photocatalysts. SiO2-Bi2MoO6, SiO2-TiO2 and SiO2-CuO composite films were prepared in a similar way to demonstrate the versatility of the proposed preparation strategy.

  9. Effects of Thermal Annealing on the Thermoelectric and Optical Properties of SiO2/SiO2+Cu Nanolayer Thin Films

    NASA Astrophysics Data System (ADS)

    Budak, S.; Baker, M.; Lassiter, J.; Smith, C.; Muntele, C.; Johnson, R. B.

    2015-06-01

    We have prepared multi-nanolayer superlattice thin-film systems comprising 36 alternating layers of SiO2 and SiO2+Cu nanolayers, of total thickness approximately 300 nm, by magnetron direct current-radio frequency sputtering. To modify their thermoelectric and optical properties, the films were placed in a furnace for annealing at temperatures between 500°C and 700°C, in air, for 1 h, to form quantum nano-dots and/or quantum clusters. Atomic force microscopy was used to analyze the surface of the thin-film systems. The thermoelectric and optical properties of the systems were characterized by study of ultraviolet-visible-near infrared absorption, fluorescence, and Raman spectroscopy, and by measurement of Seebeck coefficients. Seebeck coefficients increased from -70 μV/K to -100 μV/K when the temperature was increased from 0°C to 700°C. Optical absorption spectra showed that formation of nano-dots and/or nano-clustering also occurred as the temperature was increased. Thermal annealing affected the optical and thermal properties of the multi-nanolayer thermoelectric thin-film systems in the positive direction.

  10. Effects of Thermal Annealing on the Thermoelectric and Optical Properties of SiO2/SiO2+Cu Nanolayer Thin Films

    NASA Astrophysics Data System (ADS)

    Budak, S.; Baker, M.; Lassiter, J.; Smith, C.; Muntele, C.; Johnson, R. B.

    2014-09-01

    We have prepared multi-nanolayer superlattice thin-film systems comprising 36 alternating layers of SiO2 and SiO2+Cu nanolayers, of total thickness approximately 300 nm, by magnetron direct current-radio frequency sputtering. To modify their thermoelectric and optical properties, the films were placed in a furnace for annealing at temperatures between 500°C and 700°C, in air, for 1 h, to form quantum nano-dots and/or quantum clusters. Atomic force microscopy was used to analyze the surface of the thin-film systems. The thermoelectric and optical properties of the systems were characterized by study of ultraviolet-visible-near infrared absorption, fluorescence, and Raman spectroscopy, and by measurement of Seebeck coefficients. Seebeck coefficients increased from -70 μV/K to -100 μV/K when the temperature was increased from 0°C to 700°C. Optical absorption spectra showed that formation of nano-dots and/or nano-clustering also occurred as the temperature was increased. Thermal annealing affected the optical and thermal properties of the multi-nanolayer thermoelectric thin-film systems in the positive direction.

  11. Active Antifogging Property of Monolayer SiO2 Film with Bioinspired Multiscale Hierarchical Pagoda Structures.

    PubMed

    Han, Zhiwu; Mu, Zhengzhi; Li, Bo; Wang, Ze; Zhang, Junqiu; Niu, Shichao; Ren, Luquan

    2016-09-27

    Antifogging surfaces with hydrophilic or even superhydrophilic wetting behavior have received significant attention due to their ability to reduce light scattering by film-like condensation. However, a major challenge remains in achieving high-speed antifogging performance and revealing the hydrophilic-based antifogging mechanism of glass or other transparent materials under aggressive fogging conditions. Herein, with inspiration from the fog-free property of the typical Morpho menelaus terrestris butterfly (Butler, 1866) wing scales, a monolayer SiO2 film with multiscale hierarchical pagoda structures (MHPSs) based on glass substrate was designed and fabricated using an optimized biotemplate-assisted wet chemical method without any post-treatments. The biomimetic monolayer film (BMF) composed of nanoscale SiO2 3D networks displayed excellent antifogging properties, which is superior to that of the glass substrate itself. The MHPS-based BMF even kept high transmittance (∼95%) under aggressive fog conditions, and it almost instantaneously recovered to a fog-free state (<5 s). Moreover, the underlying active antifogging strategy gathering initial fog capture and final antifog together was revealed. The fogdrops spontaneously adhered on the BMF surface and rapidly spread along the MHPSs in an anisotropic way, which made the fogdrops evaporate instantaneously to attain an initial fog-free state, leading to an efficient active antifogging performance. These properties mainly benefit from the synergistic effect of both hydrophilic chemical compositions (nanoscale SiO2) and physical structures (biomimetic MHPSs) of the BMF. High-speed active antifogging performance of the glass materials enabled the retention of a high transmittance property even in humid conditions, heralding reliable optical performance in outdoor practical applications, especially in aggressive foggy environments. More importantly, the investigations in this work offer a promising way to handily

  12. TiO2 nanoparticles doped SiO2 films with ordered mesopore channels: a catalytic nanoreactor.

    PubMed

    Saha, Jony; Mitra, Anuradha; Dandapat, Anirban; De, Goutam

    2014-04-07

    Titanium dioxide (TiO2) incorporated ordered 2D hexagonal mesoporous silica (SiO2) films on a glass substrate were fabricated for use as a catalytic nanoreactor. Films were prepared using a tetraethyl orthosilicate (TEOS) derived SiO2 sol and a commercially available dispersion of TiO2 nanoparticles (NPs) in the presence of pluronic P123 as the structure directing agent. The effect of TiO2 doping (4-10 mol% with respect to the equivalent SiO2) into the ordered mesoporous SiO2 matrix was thoroughly investigated. The undoped SiO2 film showed a mesostructural transformation after heat-treatment at 350 °C whereas incorporation of TiO2 restricted such a transformation. Among all the TiO2 incorporated films, TEM showed that the 7 equivalent mol% TiO2 doped SiO2 film (ST-7) had an optimal composition which could retain the more organized 2D hexagonal (space group p6mm)-like mesostructures after heat-treatment. The catalytic activities of the TiO2 doped (4-10 mol%) films were investigated for the reduction of toxic KMnO4 in an aqueous medium. ST-7 film showed the maximum catalytic activity, as well as reusability. A TEM study on the resultant solution after KMnO4 reduction revealed the formation of MnO2 nanowires. It was understood that the embedded TiO2 NPs bonded SiO2 matrix increased the surface hydroxyl groups of the composite films resulting in the generation of acidic sites. The catalytic process can be explained by this enhanced surface acidity. The mesoporous channel of the ST-7 films with TiO2 doping can be used as a nanoreactor to form extremely thin MnO2 nanowires.

  13. Magnetic excitations in (SiO 2)Co nano-composite films: Brillouin light scattering study

    NASA Astrophysics Data System (ADS)

    Stashkevich, A. A.; Roussigné, Y.; Stognij, A. I.; Novitskii, N. I.; Wurtz, G.; Zayats, A. V.; Viau, G.; Chaboussant, G.; Ott, F.; Lutsev, L. V.; Djemia, P.; Kostylev, M. P.; Belotelov, V.

    2009-04-01

    Behaviour of magnetic excitations in the Damon-Eshbach (DE) and backward volume (BV) geometries in nano-composite (SiO 2) 100-xCo x (50% at< x<80% at) films has been studied by Brillouin light scattering (BLS). It has been shown that it is the structure of Stokes/anti-Stokes BLS lines in the DE geometry that allows reliable identification of dipole-exchange spin waves (SW) and numerical estimation of the value of the effective exchange constant A eff of a super-ferromagnetic nano-granular sample ( x=80% at).

  14. Controlling the defects and transition layer in SiO2 films grown on 4H-SiC via direct plasma-assisted oxidation

    NASA Astrophysics Data System (ADS)

    Kim, Dae-Kyoung; Jeong, Kwang-Sik; Kang, Yu-Seon; Kang, Hang-Kyu; Cho, Sang W.; Kim, Sang-Ok; Suh, Dongchan; Kim, Sunjung; Cho, Mann-Ho

    2016-10-01

    The structural stability and electrical performance of SiO2 grown on SiC via direct plasma-assisted oxidation were investigated. To investigate the changes in the electronic structure and electrical characteristics caused by the interfacial reaction between the SiO2 film (thickness ~5 nm) and SiC, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), density functional theory (DFT) calculations, and electrical measurements were performed. The SiO2 films grown via direct plasma-assisted oxidation at room temperature for 300s exhibited significantly decreased concentrations of silicon oxycarbides (SiOxCy) in the transition layer compared to that of conventionally grown (i.e., thermally grown) SiO2 films. Moreover, the plasma-assisted SiO2 films exhibited enhanced electrical characteristics, such as reduced frequency dispersion, hysteresis, and interface trap density (Dit ≈ 1011 cm‑2 · eV‑1). In particular, stress induced leakage current (SILC) characteristics showed that the generation of defect states can be dramatically suppressed in metal oxide semiconductor (MOS) structures with plasma-assisted oxide layer due to the formation of stable Si-O bonds and the reduced concentrations of SiOxCy species defect states in the transition layer. That is, energetically stable interfacial states of high quality SiO2 on SiC can be obtained by the controlling the formation of SiOxCy through the highly reactive direct plasma-assisted oxidation process.

  15. Controlling the defects and transition layer in SiO2 films grown on 4H-SiC via direct plasma-assisted oxidation

    PubMed Central

    Kim, Dae-Kyoung; Jeong, Kwang-Sik; Kang, Yu-Seon; Kang, Hang-Kyu; Cho, Sang W.; Kim, Sang-Ok; Suh, Dongchan; Kim, Sunjung; Cho, Mann-Ho

    2016-01-01

    The structural stability and electrical performance of SiO2 grown on SiC via direct plasma-assisted oxidation were investigated. To investigate the changes in the electronic structure and electrical characteristics caused by the interfacial reaction between the SiO2 film (thickness ~5 nm) and SiC, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), density functional theory (DFT) calculations, and electrical measurements were performed. The SiO2 films grown via direct plasma-assisted oxidation at room temperature for 300s exhibited significantly decreased concentrations of silicon oxycarbides (SiOxCy) in the transition layer compared to that of conventionally grown (i.e., thermally grown) SiO2 films. Moreover, the plasma-assisted SiO2 films exhibited enhanced electrical characteristics, such as reduced frequency dispersion, hysteresis, and interface trap density (Dit ≈ 1011 cm−2 · eV−1). In particular, stress induced leakage current (SILC) characteristics showed that the generation of defect states can be dramatically suppressed in metal oxide semiconductor (MOS) structures with plasma-assisted oxide layer due to the formation of stable Si-O bonds and the reduced concentrations of SiOxCy species defect states in the transition layer. That is, energetically stable interfacial states of high quality SiO2 on SiC can be obtained by the controlling the formation of SiOxCy through the highly reactive direct plasma-assisted oxidation process. PMID:27721493

  16. Preparation and characterization of transparent hydrophilic photocatalytic TiO2/SiO2 thin films on polycarbonate.

    PubMed

    Fateh, Razan; Dillert, Ralf; Bahnemann, Detlef

    2013-03-19

    Transparent hydrophilic photocatalytic TiO2 coatings have been widely applied to endow the surfaces self-cleaning properties. A mixed metal oxide (TiO2/SiO2) can enhance the photocatalytic performance improving the ability of surface adsorption and increasing the amount of hydroxyl surface groups. The present work introduces a systematic study concerning the effect of the SiO2 addition to TiO2 films on the wettability, the photocatalytic activity, the adhesion strength, and the mechanical stability of the films. Transparent hydrophilic photocatalytic TiO2/SiO2 thin films were used to coat the polycarbonate (PC) substrate which was precoated by an intermediate SiO2 layer. The TiO2/SiO2 thin film was prepared employing a bulk TiO2 powder (Sachtleben Hombikat UV 100) and different molar ratios of tetraethoxysilane in acidic ethanol. A dip-coating process was used to deposit the films onto the polycarbonate substrate. The films were characterized by UV/vis spectrophotometry, FTIR spectroscopy, ellipsometry, BET, AFM, XRD, and water contact angle measurements. The mechanical stability and the UV resistance were examined. The photocatalytic activity of the coated surface was calculated from the kinetic analysis of methylene blue photodegradation measurements and compared with the photocatalytic activity of Pilkington Activ sheet glass. The coated surfaces displayed considerable photocatalytic activity and superhydrophilicity after exposure to UV light. The addition of SiO2 results in an improvement of the photocatalytic activity of the TiO2 film reaching the highest value at molar ratio TiO2/SiO2 equal to 1:0.9. The prepared films exhibit a good stability against UV(A) irradiation.

  17. Morphology of SiO2 films as a key factor in alignment of liquid crystals with negative dielectric anisotropy

    PubMed Central

    Marino, Antigone; Otón, Eva; Bennis, Noureddine; Otón, Josè Manuel

    2016-01-01

    Control of liquid crystal (LC) orientation using a proper SiO2 alignment layer is essential for the optimization of vertically aligned nematic (VAN) displays. With this aim, we studied the optical anisotropy of thin SiO2 films by generalized ellipsometry as a function of deposition angle. The columnar SiO2 structure orientation measured by a noninvasive ellipsometry technique is reported for the first time, and its morphology influence on the LC alignment is demonstrated for large deposition angles. PMID:28144524

  18. Morphology of SiO2 films as a key factor in alignment of liquid crystals with negative dielectric anisotropy.

    PubMed

    Tkachenko, Volodymyr; Marino, Antigone; Otón, Eva; Bennis, Noureddine; Otón, Josè Manuel

    2016-01-01

    Control of liquid crystal (LC) orientation using a proper SiO2 alignment layer is essential for the optimization of vertically aligned nematic (VAN) displays. With this aim, we studied the optical anisotropy of thin SiO2 films by generalized ellipsometry as a function of deposition angle. The columnar SiO2 structure orientation measured by a noninvasive ellipsometry technique is reported for the first time, and its morphology influence on the LC alignment is demonstrated for large deposition angles.

  19. An Interfacial Europium Complex on SiO2 Nanoparticles: Reduction-Induced Blue Emission System

    PubMed Central

    Ishii, Ayumi; Hasegawa, Miki

    2015-01-01

    In this study, Eu-coated SiO2 nanoparticles have been prepared, consisting of an interfacial complex of Eu and 1,10-phenanthroline (phen) at the solid surfaces of the SiO2/Eu nanostructures. The as-prepared SiO2/Eu/phen nanoparticles exhibits sharp red emission via energy transfer from the phen to the EuIII. After sintering at 200 °C in air, the emission is tuned from red to blue. The blue emission is originated from EuII. This reduction-induced emissive phenomenon resulted from the electron-donating environment created by the surrounding phen and SiO2, which is the first reported fabrication of a stable EuII-based emissive material using mild conditions (reaction in air and at low temperature) and an organic-inorganic hybrid nanostructure. The existence of two different stable oxidation states with characteristic emissions, blue emissive EuII and red emissive EuIII, suggests significant potential applications as novel luminescent materials with inorganic-organic hybrid structures. PMID:26122318

  20. Surface acoustic wave properties of proton-exchanged LiNbO3 waveguides with SiO2 film.

    PubMed

    Kao, Kuo-Sheng; Cheng, Chien-Chuan; Chung, Chung-Jen; Chen, Ying-Chung

    2005-03-01

    Surface acoustic wave (SAW) properties of proton-exchanged (PE) z-cut lithium niobate (LiNbO3) waveguides with silicon dioxide (SiO2) film layers were investigated using octanoic acid. The distribution of hydrogen measured by secondary ion mass spectrometry (SIMS) showed a step-like profile, which was assumed to be equal to the waveguide depth (d). The SiO2 film was deposited on z-cut LiNbO3 waveguide by radio frequency (rf) magnetron sputtering. We investigated the important parameters for the design of SAW devices such as phase velocity (Vp), insertion loss (IL) and temperature coefficient of frequency (TCF) by a network analyzer using thin-film aluminum interdigital transducer electrodes on the upper SiO2 film surface. The experimental results showed that the Vp of SAW decreased slightly with the increase of h/lambda, where h was the thickness of SiO2 films and lambda was the wavelength. The IL of SAW increased with increased h/lambda. The TCF of SAW calculated from the frequency change of the output of SAW delay line showed an evident decrease with the increase of h/lambda. The TCF for PE z-cut LiNbO3 was measured to be about -54.72 ppm/degreees C at h/lambda = 0.08. It revealed that the SiO2 films could compensate and improve the temperature stability as compared with the TCF of SAW on PE samples without SiO2 film.

  1. Passivation of pigment-grade TiO2 particles by nanothick atomic layer deposited SiO2 films

    NASA Astrophysics Data System (ADS)

    King, David M.; Liang, Xinhua; Burton, Beau B.; Kamal Akhtar, M.; Weimer, Alan W.

    2008-06-01

    Pigment-grade TiO2 particles were passivated using nanothick insulating films fabricated by atomic layer deposition (ALD). Conformal SiO2 and Al2O3 layers were coated onto anatase and rutile powders in a fluidized bed reactor. SiO2 films were deposited using tris-dimethylaminosilane (TDMAS) and H2O2 at 500 °C. Trimethylaluminum and water were used as precursors for Al2O3 ALD at 177 °C. The photocatalytic activity of anatase pigment-grade TiO2 was decreased by 98% after the deposition of 2 nm SiO2 films. H2SO4 digest tests were performed to exhibit the pinhole-free nature of the coatings and the TiO2 digest rate was 40 times faster for uncoated TiO2 than SiO2 coated over a 24 h period. Mass spectrometry was used to monitor reaction progress and allowed for dosing time optimization. These results demonstrate that the TDMAS-H2O2 chemistry can deposit high quality, fully dense SiO2 films on high radius of curvature substrates. Particle ALD is a viable passivation method for pigment-grade TiO2 particles.

  2. Acid-Base Properties Of Glass Substrate And SiO2 - Bi2O3 Thin-Film Systems Obtained On It

    NASA Astrophysics Data System (ADS)

    Mal'chik, A. G.; Litovkin, S. V.; Filonov, A. V.; Ulyanova, O. V.; Gromov, V. E.

    2017-01-01

    The article describes an experimental research as a result of which SiO2 - Bi2O3 films have been synthesized of film-forming solutions based on tetraethoxysilane and bismuth nitrate (III). Acid-base properties of a glass substrate and SiO2 - Bi2O3 films obtained on it have been studied. The dependency of physical and chemical properties of SiO2 - Bi2O3 composites on their percentage composition have been revealed.

  3. Absorption enhancement in thin film a-Si solar cells with double-sided SiO2 particle layers

    NASA Astrophysics Data System (ADS)

    Chen, Le; Wang, Qing-Kang; Shen, Xiang-Qian; Chen, Wen; Huang, Kun; Liu, Dai-Ming

    2015-10-01

    Light absorption enhancement is very important for improving the power conversion efficiency of a thin film a-Si solar cell. In this paper, a thin-film a-Si solar cell model with double-sided SiO2 particle layers is designed, and then the underlying mechanism of absorption enhancement is investigated by finite difference time domain (FDTD) simulation; finally the feasible experimental scheme for preparing the SiO2 particle layer is discussed. It is found that the top and bottom SiO2 particle layers play an important role in anti-reflection and light trapping, respectively. The light absorption of the cell with double-sided SiO2 layers greatly increases in a wavelength range of 300 nm-800 nm, and the ultimate efficiency increases more than 22% compared with that of the flat device. The cell model with double-sided SiO2 particle layers reported here can be used in varieties of thin film solar cells to further improve their performances. Project supported by the National High-Tech Research and Development Program of China (Grant No. 2011AA050518), the University Research Program of Guangxi Education Department, China (Grant No. LX2014288), and the Natural Science Foundation of Guangxi Zhuang Autonomous Region, China (Grant No. 2013GXNSBA019014).

  4. Analysis of long-term internal stress and film structure of SiO2 optical thin films.

    PubMed

    Nishikawa, Toshiyuki; Ono, Hiroi; Murotani, Hiroshi; Iida, Yoshitaka; Okada, Katsuhisa

    2011-03-20

    Recently, the demand for durability of optical thin films, which have long been used, has been growing as the performance of optical components improves. The stress of a film is an important parameter that is related to its adhesion. The electron beam (EB) and ion-assisted deposition (IAD) methods are widely used to fabricate optical thin films. However, there are few reports on long-term internal stress, despite the importance of this issue. Here we discuss the time dependence of the stress of SiO2 optical thin films in terms of optical characteristics in the infrared region. It was found that SiO2 thin films prepared by the EB and IAD methods exhibited compression stress. The Si-OH molecular bond was observed at around 930 cm(-1) in the Fourier transform infrared spectroscopy spectrum of the sample prepared by the EB method, which exhibited a large change in internal stress after an elapsed time. It is considered that this change in bonding was related to the decrease in the stress of the films.

  5. Spectroscopic and electrical properties of SiO2 films prepared by simple and cost effective sol-gel process.

    PubMed

    Vishwas, M; Rao, K Narasimha; Phani, A R; Arjuna Gowda, K V; Chakradhar, R P S

    2011-02-01

    Amorphous SiO2 thin films were prepared on glass and silicon substrates by cost effective sol-gel method. Tetra ethyl ortho silicate (TEOS) was used as the precursor material, ethanol as solvent and concentrated HCl as a catalyst. The films were characterized at different annealing temperatures. The optical transmittance was slightly increased with increase of annealing temperature. The refractive index was found to be 1.484 at 550 nm. The formation of SiO2 film was analyzed from FT-IR spectra. The MOS capacitors were designed using silicon (100) substrates. The current-voltage (I-V), capacitance-voltage (C-V) and dissipation-voltage (D-V) measurements were taken for all the annealed films deposited on Si (100). The variation of current density, resistivity and dielectric constant of SiO2 films with different annealing temperatures was investigated and discussed for its usage in applications like MOS capacitor. The results revealed the decrease of dielectric constant and increase of resistivity of SiO2 films with increasing annealing temperature.

  6. Annealing effects of tantalum films on Si and SiO2/Si substrates in various vacuums

    NASA Astrophysics Data System (ADS)

    Liu, Ling; Wang, Yue; Gong, Hao

    2001-07-01

    The annealing effects of 550 nm thick β-Ta films sputtered on Si and SiO2 substrates have been investigated under various vacuum conditions. Phase transformation from the tetragonal β-Ta into body-centered-cubic α-Ta of much higher conductivity occurred at annealing temperatures lower than 500 °C and 80% of β-Ta transformed into α-Ta after annealing at 600 °C for Ta on a Si substrate. For Ta on a SiO2 substrate, no phase transformation was observed at 500 °C annealing, and only 20% of β-Ta transformed into α-Ta at 600 °C. Oxygen diffusion into the Ta film at the interface of Ta/SiO2 could hinder β-Ta to α-Ta transformation. Both Ta on Si and Ta on SiO2 samples have smooth surfaces after annealing in 2×10-5 Torr. After annealing in a vacuum lower than 2×10-4 Torr, surface oxidation of the Ta thin films was detected. The increase of oxygen content in the Ta films caused higher compressive stress, and resulted in the film peeling in a serpentine pattern during annealing at 500 °C in 2×10-2 Torr for Ta on a SiO2 substrate. The Ta films cracked and detached from the SiO2 substrate after being annealed at 750 °C in 2×10-2 Torr. In contrast, no crack was found in Ta on Si, probably because of the relief of film stress due to more β-Ta being transformed into α-Ta during annealing. The residual oxygen and moisture in low vacuum may build up stress in Ta thin films during thermal processes, which can cause major reliability problems in electronic and other applications.

  7. Role of HfO2/SiO2 thin-film interfaces in near-ultraviolet absorption and pulsed laser damage

    DOE PAGES

    Papernov, Semyon; Kozlov, Alexei A.; Oliver, James B.; ...

    2016-07-15

    Here, the role of thin-film interfaces in the near-ultraviolet (near-UV) absorption and pulsed laser-induced damage was studied for ion-beam-sputtered and electron-beam-evaporated coatings comprised from HfO2 and SiO2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO2 single-layer film and for a film containing seven narrow HfO2 layers separated by SiO2 layers. The seven-layer film was designed to have a total optical thickness of HfO2 layers, equal to one wave at 355 nm and an E-field peak and average intensity similarmore » to a single-layer HfO2 film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces as compared to HfO2 film material. The relevance of obtained absorption data to coating near-UV, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO2 film in both sputtered and evaporated coatings. The results are explained through the similarity of interfacial film structure with structure formed during the codeposition of HfO2 and SiO2 materials.« less

  8. Effect of the working gas of the ion-assisted source on the optical and mechanical properties of SiO2 films deposited by dual ion beam sputtering with Si and SiO2 as the starting materials.

    PubMed

    Wu, Jean-Yee; Lee, Cheng-Chung

    2006-05-20

    Silicon and fused-silica targets are used as the starting materials for depositing silicon oxide (SiO2) films. The SiO2 films are prepared by a dual ion beam sputtering deposition system with a main ion source and an ion-assisted source with different working gases. The films deposited are then examined and compared by using a visible spectrophotometer, a Fourier-transform IR spectrophotometer, an atomic force microscope, and contact angle instruments. A Twyman-Green interferometer is employed to study the film stress by phase-shift interferometry. All the SiO2 films show excellent optical properties with extra-low extinction coefficients (below 2x10(-5)) and have no water absorption. When the working gas is O2 for the ion-assisted source, the deposited SiO2 films show good properties in terms of stress and roughness and with a good molecular bonding structure order for both targets. However, SiO2 films deposited from the fused-silica target had a larger contact angle, while those deposited from the silicon target had 2.5 times the deposition rate.

  9. Mechanism of charging of Au atoms and nanoclusters on Li doped SiO2/Mo(112) films.

    PubMed

    Martinez, Umberto; Giordano, Livia; Pacchioni, Gianfranco

    2010-02-01

    We present the results of supercell DFT calculations on the adsorption properties of Au atoms and small clusters (Au(n), n < or = 5) on a SiO(2)/Mo(112) thin film and on the same system modified by doping with Li atoms. The adsorbed Li atoms penetrate into the pores of the silica film and become stabilized at the interface where they donate one electron to the Mo metal. As a consequence, the work function of the Li-doped SiO(2)/Mo(112) film is reduced and results in modified adsorption properties. In fact, while on the undoped SiO(2)/Mo(112) film Au interacts only very weakly, on the Li-doped surface Au atoms and clusters bind with significant bond strengths. The calculations show that this is due to the occurrence of an electron transfer from the SiO(2)/Mo(112) interface to the adsorbed gold. The occurrence of the charge transfer is related to the work function of the support but also to the possibility for the silica film to undergo a strong polaronic distortion.

  10. Improved Performance by SiO2 Hollow Nanospheres for Silver Nanowire-Based Flexible Transparent Conductive Films.

    PubMed

    Zhang, Liwen; Zhang, Longjiang; Qiu, Yejun; Ji, Yang; Liu, Ya; Liu, Hong; Li, Guangji; Guo, Qiuquan

    2016-10-12

    Flexible transparent conductive films (TCFs) have attracted tremendous interest thanks to the rapid development of portable/flexible/wearable electronics. TCFs on the basis of silver nanowires (AgNWs) with excellent performance are becoming an efficient alternative to replace the brittle transparent metal oxide. In this study, a promising method was developed by introducing SiO2 hollow nanospheres (SiO2-HNSs) into the film to significantly improve the performance of AgNW-based TCFs. Since SiO2-HNSs have opposite charges to AgNWs, the strong attraction had promoted a uniform distribution of AgNWs and made the distance between AgNWs closer, which could decrease the contact resistance greatly. The introduction of SiO2 layer remarkably enhanced the transmission of visible light and the conductivity. In addition, the TCFs constructed by AgNWs and SiO2-HNSs showed much higher thermal stability and adhesive force than those by only AgNWs. As an example, the transmission of AgNW/SiO2-HNS-coated poly(ethylene terephthalate) (PET) could increase about 14.3% in comparison to AgNW-coated PET. Typically, a AgNW/SiO2-HNS-based TCF with a sheet resistance of about 33 Ω/sq and transmittance of about 98.0% (excluding substrate) could be obtained with excellent flexibility, adhesion, and thermal stability. At last some devices were fabricated.

  11. THz pulse generation using a contact grating device composed of TiO2/SiO2 thin films on LiNbO3 crystal

    NASA Astrophysics Data System (ADS)

    Yoshida, Fumiko; Nagashima, Keisuke; Tsubouchi, Masaaki; Maruyama, Momoko; Ochi, Yoshihiro

    2016-11-01

    We developed a new contact grating device for terahertz (THz) pulse generation by optical rectification. The device was made from polycrystalline rutile TiO2 thin film in the grating region and an amorphous SiO2 layer deposited on a Mg-doped LiNbO3 crystal. Our calculations indicated that the TiO2 grating on the SiO2 layer would yield an increase in diffraction efficiency of up to 0.69. The prepared TiO2 thin film had a sufficient laser induced damage threshold (140 GW/cm2) to enable effective THz pulse generation. Using a prototype device, we demonstrated THz pulse generation and investigated the phase-matching conditions experimentally.

  12. Solution-processed crack-free oxide films formed using SiO2 nanoparticles and organoalkoxysiloxane precursors

    NASA Astrophysics Data System (ADS)

    Na, Moonkyong; Rhee, Shi-Woo

    2015-07-01

    Crack-free uniform oxide films were deposited by spin-on-glass method using a mixture solution of organoalkoxysiloxane network former and SiO2 nanoparticles. In the range of molar ratio of SiO2 nanoparticles to oragnoalkoxysiloxanes between 0.6:1 and 1:1, stable sols were formed and smooth and uniform oxide films could be obtained. Fourier-transform infrared (FT-IR) spectroscopy was used to investigate the chemical properties of the films, and we found that Sisbnd Osbnd Si structures were effectively formed via condensation reactions during curing at 150 °C. The effect of three different organic side groups in the organoalkoxsiloxane on the film properties was investigated. Precursors containing methyl groups effectively formed Sisbnd Osbnd Si network with SiO2 nanoparticles, which was confirmed by the increased intensity of the Sisbnd O asymmetric stretching mode at 1080 cm-1 in the FT-IR spectra. Smooth and continuous films were obtained using precursors containing methyl and phenyl groups, with root-mean-square surface roughness of 1.05 nm (methyl precursor) and 1.16 nm (phenyl precursor). The shrinkage of the oxide film formed with phenyl groups was less than 1%. The dielectric properties of the oxide films were characterized, and we observed leakage currents in the range of 10-9 to 10-8 A/cm2 just prior to the dielectric breakdown with the films formed using precursors containing methyl and phenyl groups

  13. Laser-induced damage of TiO2/SiO2 high reflector at 1064 nm

    NASA Astrophysics Data System (ADS)

    Yao, Jianke; Ma, Jianyong; Xiu, Cheng; Fan, Zhengxiu; Jin, Yunxia; Zhao, Yuanan; He, Hongbo; Shao, Jianda; Huang, Huolin; Zhang, Feng; Wu, Zhengyun

    2008-04-01

    A high laser-induced damage threshold (LIDT) TiO2/SiO2 high reflector (HR) at 1064nm is deposited by e-beam evaporation. The HR is characterized by optical properties, surface, and cross section structure. LIDT is tested at 1064nm with a 12ns laser pulse in the one-on-one mode. Raman technique and scanning electron Microscope are used to analyze the laser-induced modification of HR. The possible damage mechanism is discussed. It is found that the LIDT of HR is influenced by the nanometer precursor in the surface, the intrinsic absorption of film material, the compactness of the cross section and surface structure, and the homogeneity of TiO2 layer. Three typical damage morphologies such as flat-bottom pit, delamination, and plasma scald determine well the nanometer defect initiation mechanism. The laser-induced crystallization consists well with the thermal damage nature of HR.

  14. Optical and Structural Properties of Si Nanocrystals in SiO2 Films

    PubMed Central

    Nikitin, Timur; Khriachtchev, Leonid

    2015-01-01

    Optical and structural properties of Si nanocrystals (Si-nc) in silica films are described. For the SiOx (x < 2) films annealed above 1000 °C, the Raman signal of Si-nc and the absorption coefficient are proportional to the amount of elemental Si detected by X-ray photoelectron spectroscopy. A good agreement is found between the measured refractive index and the value estimated by using the effective-medium approximation. The extinction coefficient of elemental Si is found to be between the values of crystalline and amorphous Si. Thermal annealing increases the degree of Si crystallization; however, the crystallization and the Si–SiO2 phase separation are not complete after annealing at 1200 °C. The 1.5-eV PL quantum yield increases as the amount of elemental Si decreases; thus, this PL is probably not directly from Si-nc responsible for absorption and detected by Raman spectroscopy. Continuous-wave laser light can produce very high temperatures in the free-standing films, which changes their structural and optical properties. For relatively large laser spots, the center of the laser-annealed area is very transparent and consists of amorphous SiO2. Large Si-nc (up to ~300 nm in diameter) are observed in the ring around the central region. These Si-nc lead to high absorption and they are typically under compressive stress, which is connected with their formation from the liquid phase. By using strongly focused laser beams, the structural changes in the free-standing films can be made in submicron areas.

  15. Epitaxial Growth of Silicon Films on SiO2 Patterned Si(100) Substrates by Atmospheric Pressure Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Duan, Chunyan; Deng, Youjun; Ai, Bin; Liu, Chao; Zhuang, Lin; Shen, Hui

    2012-09-01

    In order to investigate the effect of selective area nucleation on epitaxial growth of silicon (Si) films, 35 µm thick Si films were deposited by atmospheric pressure chemical vapor deposition (APCVD) under the standard condition on two kinds of SiO2 patterned Si(100) wafers. One was circular patterns, and the other was striated patterns. Then, the structural properties of the as-deposited silicon thin films were investigated by metallurgical microscope, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM). The results show that normal epitaxial growth occurs on the exposed Si(100) regions, while just polycrystalline Si deposition happens on the SiO2 regions. Moreover, for the substrates with circular patterns, the as-deposited Si thin films possess pyramid surface morphology thus excellent light trapping performance being spontaneously formed, and the sizes of the pyramid grains approximately equal to the sum of the diameter and spacing of the round exposed Si regions.

  16. High speed deposition of SiO2 film by slot-type microwave CVD system

    NASA Astrophysics Data System (ADS)

    Toyoda, Hirotaka; Yamamoto, Masaki; Suzuki, Haruka

    2016-09-01

    High density microwave plasma is attractive because of its ability for high-throughput processing. So far, we have successfully produced large-area surface wave excited plasma (SWP) and have applied it to plasma-enhanced chemical vapor deposition (PE-CVD) of silicon films. However, the SWP requires a dielectric plate for the surface wave propagation, and high density plasma sometimes erodes the dielectric plate to produce oxygen contamination. To avoid such problem, we propose the PE-CVD using the microwave plasma produced inside slots of a waveguide without using the dielectric plate. A 2.45 GHz pulsed microwave (repetition: 20 kHz, duty ratio: 20%, average power: 40 W) is introduced to a rectangular waveguide through an isolator, a tuner, and a vacuum window. A slot of 4 mm in length and 0.2 mm in width is placed at the end of the waveguide, and is connected to a vacuum chamber. Both the waveguide and the chamber are evacuated by a turbomolecular pump. Oxygen and tetraethyl orthosilicate (TEOS) gases are introduced from the waveguide and from the outside of the waveguide, respectively, to deposit SiO2 film on Si substrates at a pressure of 15 Torr and a slot-substrate distance of 1.1 cm. Deposition rate as high as 80 nm/s is observed at a TEOS flow rate of 0.8 sccm. The result suggests that the present PE-CVD system is promising as a new high-speed film deposition technique. Part of this work is supported by JSPS KAKENHI Grant Number 25286079.

  17. Recrystallization of Ge thin film on SiO2 substrates using a two-step annealing process

    NASA Astrophysics Data System (ADS)

    Kim, Sung Wook; Lee, Jaejun; Park, Youn Ho; Park, Jeong Min; Do, Hong Kyeong; Kim, Yeon Joo; Choi, Heon-Jin

    2017-01-01

    The fabrication of high-quality crystalline germanium thin films (GeTF) on an amorphous SiO2 layer is crucial for the realization of high performance-, low cost III-V solar cells used in many applications. Herein, we report the growth of a high-quality crystalline GeTF on SiO2/Si substrates using an ultra-vacuum chemical vapor deposition (UHV-CVD) method. GeTF was grown on the SiO2 layer using a two-step growth and multi-annealing processes. The fabrication method involved the deposition of a 1st seeding layer, annealing, and deposition of a 2nd main layer followed by three times of cyclic annealing. The crystallization of the seeding layer having a thickness of less than 10 nm could be ascribed to the evolution of polycrystalline structures in the main layer. The cyclic annealing performed after the deposition of the main layer is also found to be crucial for the formation of single crystalline, high-quality Ge films on SiO2 substrates with <311> direction. The cyclic annealing results in a further reduction of the defects, thereby threading dislocations significantly to a density of 5.311 × 107 cm-2. Electrical measurements using the van der Pauw method revealed that the GeTF exhibits p-type characteristics and a high mobility of 360.10 cm2/Vs at room temperature. [Figure not available: see fulltext.

  18. Thermal oxidation of amorphous germanium thin films on SiO2 substrates

    NASA Astrophysics Data System (ADS)

    de los Santos Valladares, L.; Bustamante Dominguez, A.; Ionescu, A.; Brown, A.; Sepe, A.; Steiner, U.; Avalos Quispe, O.; Holmes, S.; Majima, Y.; Langford, R.; Barnes, C. H. W.

    2016-12-01

    In this work we report the thermal oxidation of amorphous germanium (a-Ge) thin films (140 nm thickness) in air. Following fabrication by conventional thermal evaporation on SiO2 substrates, the samples were annealed in air at different temperatures ranging from 300 to 1000 °C. By means of x-ray diffraction, x-ray reflectivity, synchrotron grazing-incidence wide-angle x-ray scattering and cross-sectional transmission electron microscopy analysis it is found that the a-Ge films abruptly crystallize at 475 °C, while simultaneously increasing the thickness of the oxide (GeO2) in a layer by layer fashion. X-ray photoemission spectroscopy reveals that the oxidation state of the Ge atoms in the GeO2 layer is 4+. However, a reaction at the GeO2/Ge interface occurs between 500 and 550 °C reducing the oxide layer to GeO x (x < 2) and containing Ge2+ and Ge+. The thickness of the oxide layer grows with the annealing temperature following an Arrhenius behavior with an activation energy of 0.82 ± 0.09 eV up to 500 °C. Remarkably, we observed simultaneous enhancement of the oxidation and crystallization of the a-Ge in the temperature interval 450 °C-500 °C, in which the oxidation rate reaches a maximum of around 0.8 nm °C-1 at around 500 °C.

  19. Self-assembled dual in-plane gate thin-film transistors gated by nanogranular SiO2 proton conductors for logic applications

    NASA Astrophysics Data System (ADS)

    Zhu, Li Qiang; Sun, Jia; Wu, Guo Dong; Zhang, Hong Liang; Wan, Qing

    2013-02-01

    Phosphorus (P)-doped nanogranular SiO2 films are deposited by plasma-enhanced chemical vapor deposition at room temperature, and a high proton conductivity of ~5.6 × 10-4 S cm-1 is measured at room temperature with a relative humidity of 70%. The accumulation of protons at the SiO2/indium-zinc-oxide (IZO) interface induces a large electric-double-layer (EDL) capacitance. Thin-film transistors (TFTs) with two in-plane gates are self-assembled on transparent conducting glass substrates. The large EDL capacitance can effectively modulate the IZO channel with a current ON/OFF ratio of >107. Such TFTs calculate dual input signals at the gate level coupled with a floating gate, analogous to that of neuron MOS (vMOS). AND logic is demonstrated on the neuron TFTs. Such neuron TFTs gated by P-doped nanogranular SiO2 shows an effective electrostatic modulation on conductivities of oxide semiconductors, which is meaningful for portable chemical-biological sensing applications.

  20. Self-assembled dual in-plane gate thin-film transistors gated by nanogranular SiO2 proton conductors for logic applications.

    PubMed

    Zhu, Li Qiang; Sun, Jia; Wu, Guo Dong; Zhang, Hong Liang; Wan, Qing

    2013-03-07

    Phosphorus (P)-doped nanogranular SiO(2) films are deposited by plasma-enhanced chemical vapor deposition at room temperature, and a high proton conductivity of ~5.6 × 10(-4) S cm(-1) is measured at room temperature with a relative humidity of 70%. The accumulation of protons at the SiO(2)/indium-zinc-oxide (IZO) interface induces a large electric-double-layer (EDL) capacitance. Thin-film transistors (TFTs) with two in-plane gates are self-assembled on transparent conducting glass substrates. The large EDL capacitance can effectively modulate the IZO channel with a current ON/OFF ratio of >10(7). Such TFTs calculate dual input signals at the gate level coupled with a floating gate, analogous to that of neuron MOS (vMOS). AND logic is demonstrated on the neuron TFTs. Such neuron TFTs gated by P-doped nanogranular SiO(2) shows an effective electrostatic modulation on conductivities of oxide semiconductors, which is meaningful for portable chemical-biological sensing applications.

  1. Nanostructured Er3+-doped SiO2-TiO2 and SiO2-TiO2-Al2O3 sol-gel thin films for integrated optics

    NASA Astrophysics Data System (ADS)

    Predoana, Luminita; Preda, Silviu; Anastasescu, Mihai; Stoica, Mihai; Voicescu, Mariana; Munteanu, Cornel; Tomescu, Roxana; Cristea, Dana

    2015-08-01

    The nanostructured multilayer silica-titania or silica-titania-alumina films doped with Er3+ were prepared by sol-gel method. The sol-gel method is a flexible and convenient way to prepare oxide films on several types of substrates, and for this reason it was extensively investigated for optical waveguides fabrication. The selected molar composition was 90%SiO2-10%TiO2 or 85%SiO2-10%TiO2-5% Al2O3 and 0.5% Er2O3. The films were characterized by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Spectroellipsometry (SE), as well as by Atomic Force Microscopy (AFM) and photoluminescence (PL). The films deposited on Si/SiO2 substrate by dip-coating or spin-coating, followed by annealing at 900 °C, presented homogenous and continuous surface and good adherence to the substrate. Differences were noticed in the structure and properties of the prepared films, depending on the composition and the number of deposited layers. Channel optical waveguides were obtained by patterning Er3+-doped SiO2-TiO2 and SiO2-TiO2-Al2O3 sol-gel layers deposited on oxidized silicon wafers.

  2. Density relative change and interface zone mutual diffusion of BiFeO3 films prepared on Si (1 0 0), SiO2 and SiO2/Si (1 0 0)

    NASA Astrophysics Data System (ADS)

    Xiao, RenZheng; Wang, ZeSong; Yuan, XianBao; Zhou, JianJun; Mao, ZhangLiang; Su, HuaShan; Li, Bo; Fu, DeJun

    2016-10-01

    The mutual diffusion taken place in the interface zone between BiFeO3 (BFO) films and substrates (Si (1 0 0), SiO2 and SiO2/Si (1 0 0)) has been revealed by energy dispersive X-ray spectroscopy (EDS) and Rutherford Backscattering Spectrometry (RBS). RBS spectra provide the relative atomic concentrations of Bi, Fe, Si, and O elements changed with the samples' depth as analyzed by RBS spectra fitting SIMNRA software. A certain width of the intermixing layer is probably formed between BFO films and individual substrate which is attributed to mutual diffusion in the interface zone during annealing process. The mechanism of concerted exchange component can explain the interface zone mutual diffusion phenomenon between BFO films and substrates. The width of the interface zone between BFO film and Si (1 0 0), SiO2, and SiO2/Si (1 0 0) substrate is about 1.94 × 1017, 2.01 × 1017 and 3.05 × 1017 atoms/cm2, respectively, which are equivalent to 30.9, 36.7, and 52.9 nm, respectively. It has been declared that the effect on density relative to BFO film is loosen or attenuation is presented in the interface zone, which can be interpreted as a migration or diffusion of various atoms during the annealing. This can also provide an evidence of atomic dynamics and defect engineering on interface diffusion.

  3. Diffraction Properties of Volume Holograms Recorded in SiO2 Nanoparticle-Dispersed Methacrylate Photopolymer Films

    NASA Astrophysics Data System (ADS)

    Suzuki, Naoaki; Tomita, Yasuo

    2003-08-01

    We report on holographic recording in the green with high diffraction efficiency and recording sensitivity in SiO2 nanoparticle-dispersed methacrylate photopolymer films. Dynamics of diffraction efficiencies and refractive index changes are measured for several SiO2 nanoparticle concentrations and grating spacings. Overmodulation phenomena in the diffraction efficiency are observed in films with the effective thickness of ˜32 μm and high nanoparticle concentrations. It is confirmed that the performance of this material system as holographic recording media is comparable to that of recently reported methacrylate photopolymers doped with TiO2 nanoparticles [N. Suzuki, Y. Tomita and T. Kojima: Appl. Phys. Lett. 81 (2002) 4121].

  4. Nanodimple Arrays Fabricated on SiO2 Surfaces by Wet Etching through Block Copolymer Thin Films

    NASA Astrophysics Data System (ADS)

    Watanabe, Ryoko; Kamata, Kaori; Iyoda, Tomokazu

    2008-06-01

    Block copolymer thin films are promising nanotemplates because highly ordered periodic structures are spontaneously formed through microphase separation on a deca-nanometer scale and over a large area. An amphiphilic block copolymer, which consists of poly(ethylene oxide) (PEO) and poly(methacrylate) (PMA) with azobenzene mesogens and is denoted by PEOm-b-PMA(Az)n, indicates a strong chemical contrast between the corresponding microdomains, which offer structurally reliable nanotemplates for fabricating nanostructured materials. Thermally annealing a PEOm-b-PMA(Az)n thin film provides hexagonally arranged, perpendicularly oriented PEO cylinders, which perform as ion-conductive nanochannels. In this study, a SiO2 layer on a silicon wafer substrate is etched by NH4F through a PEO114-b-PMA(Az)54 thin film as a nanomask. The SiO2 layer is patterned with a 24-nm-periodic hexagonally arranged nanodimple array. Atomic force microscope (AFM), field emission scanning electron microscope (FESEM), and cross-sectional transmission electron microscope (TEM) observations reveal that the nanodimple array has a 2-nm depth and is spread over the entire SiO2 surface on centimeter scale.

  5. Electroluminescence and Photoluminescence from Scored Si-Rich SiO2 Film/p-Si Structure

    NASA Astrophysics Data System (ADS)

    Ran, Guang-Zhao; Sun, Yong-Ke; Chen, Yuan; Dai, Lun; Cui, Xiao-Ming; Zhang, Bo-Rui; Qiao, Yong-Ping; Ma, Zhen-Chang; Zong, Wan-Hua; Qin, Guo-Gang

    2003-02-01

    Electroluminescence (EL) is observed from the Au/Si-rich SiO2 film/p-Si diodes, in which the Si-rich SiO2 films are scored deliberately by a diamond tip. The EL intensity of the scored diode annealed at 800°C is about 6 times of that of the unscored counterpart. The EL spectrum of the unscored diode could be decomposed into two Gaussian luminescence bands with peaks at about 1.83 and 2.23 eV, while for the EL spectrum of the scored diode, an additional Gaussian band at about 3.0 eV appears, and the 1.83-eV peak increases significantly in intensity. The photoluminescence (PL) spectrum of an unscored Si-rich SiO2 film has only one band peaking at about 1.48 eV, whereas the PL spectrum of the scored one has two bands at about 1.48 and 1.97 eV. We consider that the high-density defect regions produced by the scoring provide new luminescence centres and become some types of nonradiative centres in the Si oxide layer, which thus result in changes of the EL and PL spectra.

  6. Shift in room-temperature photoluminescence of low-fluence Si(+)-implanted SiO2 films subjected to rapid thermal annealing.

    PubMed

    Fu, Ming-Yue; Tsai, Jen-Hwan; Yang, Cheng-Fu; Liao, Chih-Hsiung

    2008-12-01

    We experimentally demonstrate the effect of the rapid thermal annealing (RTA) in nitrogen flow on photoluminescence (PL) of SiO2 films implanted by different doses of Si(+) ions. Room-temperature PL from 400-nm-thick SiO2 films implanted to a dose of 3×10(16) cm(-2) shifted from 2.1 to 1.7 eV upon increasing RTA temperature (950-1150 °C) and duration (5-20 s). The reported approach of implanting silicon into SiO2 films followed by RTA may be effective for tuning Si-based photonic devices.

  7. Preparation of Ag/TiO2/SiO2 films via photo-assisted deposition and adsorptive self-assembly for catalytic bactericidal application

    NASA Astrophysics Data System (ADS)

    Xi, Baojuan; Chu, Xiaona; Hu, Jiangyong; Bhatia, Charanjit Singh; Danner, Aaron James; Yang, Hyunsoo

    2014-08-01

    The deterioration of water supply quality due to the waterborne bacteria is an environmental problem requiring the urgent attention. Due to the excellent and synergic antimicrobial capability, Ag-loaded TiO2 photocatalyst emerges as a feasible measure to guard the water. In our work, Ag nanoparticles have been prepared by the photoassisted reduction of AgNO3 on the TiO2 film fabricated by solution-based adsorptive self-assembly approach. The role of surfactant on the growth rate and size controlling of particles is also studied. In this connection, different kinds of surfactants, such as PVP, Tween-20, Tween-40 and so on, are applied in the system to investigate the formation of Ag nanoparticles. The surface profile and elemental analysis of Ag/TiO2/SiO2 films are examined by scanning electron microscopy and attached energy-dispersive X-ray spectroscopy, respectively. In the anti-bacteria detection, Ag nanoparticles are found to enhance the bactericidal efficiency strongly comparing with the pure TiO2 film under the same condition. In addition, by comparison with Ag/TiO2/SiO2 film in the dark environment as the reference experiment, UV-visible light plays a vital role in the improved bactericidal behavior, demonstrating the more efficient charge separation induced by metal silver. Because of the versatility of the method, the present photoreductive route is also exploited for the synthesis of Au nanoparticles on TiO2/SiO2 films. The corresponding photocatalytical detection results demonstrate the loading of Au nanoparticles can improve the photodegradation efficiency of methyl orange assigned to the similar electron-trapping effect to silver.

  8. Electronic sputtering of thin SiO 2 films by MeV heavy ions

    NASA Astrophysics Data System (ADS)

    Arnoldbik, W. M.; Tomozeiu, N.; Habraken, F. H. P. M.

    2003-04-01

    The rate of removal of material from SiO 2 as a result of heavy ion irradiation, with energies in which energy loss via excitation and ionization of the solid predominates, depends strongly on the stopping power and angle of incidence of the incoming ions. There appears to be a threshold stopping power for SiO 2 of 500 eV/(10 15 at/cm 2) (or 3.5 keV/nm). This electronic sputter yield has been found to reach values as large as 10 4 atoms/incoming ion for 66 MeV Ag ions at an angle of incidence of 7° with the plane of the surface. Strikingly, the electronic sputter yield is very small for thin SiO 2 layers of a thickness ⩽1 nm when grown on c-Si, but it is appreciable for such layers deposited on the insulator silicon nitride. The data are discussed in the light of existing models for electronic sputtering invoking also models for potential sputtering of SiO 2 by low-energy, highly charged ions.

  9. Hollow waveguides with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films

    PubMed Central

    Zhao, Y.; Jenkins, M.; Measor, P.; Leake, K.; Liu, S.; Schmidt, H.; Hawkins, A. R.

    2011-01-01

    A type of integrated hollow core waveguide with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films is demonstrated. Hollow core waveguides made with a combination of plasma-enhanced chemical vapor deposition SiO2 and sputtered Ta2O5 provide a nearly optimal structure for optofluidic biofluorescence measurements with low optical loss, high fabrication yield, and low background photoluminescence. Compared to earlier structures made using Si3N4, the photoluminescence background of Ta2O5 based hollow core waveguides is decreased by a factor of 10 and the signal-to-noise ratio for fluorescent nanobead detection is improved by a factor of 12. PMID:21448254

  10. Hollow waveguides with low intrinsic photoluminescence fabricated with Ta(2)O(5) and SiO(2) films.

    PubMed

    Zhao, Y; Jenkins, M; Measor, P; Leake, K; Liu, S; Schmidt, H; Hawkins, A R

    2011-02-28

    A type of integrated hollow core waveguide with low intrinsic photoluminescence fabricated with Ta(2)O(5) and SiO(2) films is demonstrated. Hollow core waveguides made with a combination of plasma-enhanced chemical vapor deposition SiO(2) and sputtered Ta(2)O(5) provide a nearly optimal structure for optofluidic biofluorescence measurements with low optical loss, high fabrication yield, and low background photoluminescence. Compared to earlier structures made using Si(3)N(4), the photoluminescence background of Ta(2)O(5) based hollow core waveguides is decreased by a factor of 10 and the signal-to-noise ratio for fluorescent nanobead detection is improved by a factor of 12.

  11. Hollow waveguides with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Jenkins, M.; Measor, P.; Leake, K.; Liu, S.; Schmidt, H.; Hawkins, A. R.

    2011-02-01

    A type of integrated hollow core waveguide with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films is demonstrated. Hollow core waveguides made with a combination of plasma-enhanced chemical vapor deposition SiO2 and sputtered Ta2O5 provide a nearly optimal structure for optofluidic biofluorescence measurements with low optical loss, high fabrication yield, and low background photoluminescence. Compared to earlier structures made using Si3N4, the photoluminescence background of Ta2O5 based hollow core waveguides is decreased by a factor of 10 and the signal-to-noise ratio for fluorescent nanobead detection is improved by a factor of 12.

  12. Comparison of the Sputter Rates of Oxide Films Relative to the Sputter Rate of SiO2

    SciTech Connect

    Baer, Donald R.; Engelhard, Mark H.; Lea, Alan S.; Nachimuthu, Ponnusamy; Droubay, Timothy C.; Kim, J.; Lee, B.; Mathews, C.; Opila, R. L.; Saraf, Laxmikant V.; Stickle, William F.; Wallace, Robert; Wright, B. S.

    2010-09-02

    Because of the increasing technological importance of oxide films for a variety of applications, there is a growing interest in knowing the sputter rates for a wide variety of oxides. To support needs of users of the Environmental Molecular Sciences Laboratory (EMSL) User facility as well as our research programs, we have made a series of measurements of the sputter rates for oxide films that have been grown by oxygen plasma assisted molecular beam epitaxy (OPA-MBE), pulsed laser deposition (PLD), Atomic Layer Deposition (ALD), electrochemical oxidation, or sputter deposition. The sputter rates for these oxide films were determined in comparison to the sputter rates for thermally grown SiO2, a common sputter rate reference material. The film thicknesses and densities of these films were usually measured using x-ray reflectivity (XRR). These samples were mounted in an x-ray photoelectron spectroscopy (XPS) system or an Auger electron spectrometer for sputtering measurements using argon ion sputtering. Although the primary objective was to determine relative sputter rates at a fixed angle, the measurements were also used to determine: i) the angle dependence of the relative sputter rates; ii) the energy dependence of the relative sputter rates; and iii) the extent of ion beam reduction for the various oxides. Materials examined include: SiO2 (reference films), Al2O3, CeO2, Cr2O3, Fe2O3, HfO2, ITO (In-Sn-oxide) Ta2O5, TiO2 (anatase and rutile) and ZnO. We find that the sputter rates for the oxides can vary up to a factor of two (usually slower) from that observed for SiO2. The ratios of sputter rates to SiO2 appear to be relatively independent of ion beam energy for the range of 1kV to 4 kV and for incident angles of less than 50º. As expected, the ion beam reduction of the oxides varies with the sputter angle. These studies demonstrate that we can usually obtain sputter rate reproducibility better than 5% for similar oxide films.

  13. Well-organized meso-macroporous TiO2/SiO2 film derived from amphiphilic rubbery comb copolymer.

    PubMed

    Jeon, Harim; Lee, Chang Soo; Patel, Rajkumar; Kim, Jong Hak

    2015-04-15

    We report the facile synthesis of a well-organized meso-macroporous TiO2/SiO2 thin film with high porosity and good interconnectivity from a binary mixture (i.e., titania precursor and polymer template). Our process is based on self-assembly of the amphiphilic rubbery comb copolymer, poly(dimethylsiloxane)-g-poly(oxyethylene methacrylate) (PDMS-g-POEM) with titanium tetraisopropoxide (TTIP). SiO2 is self-provided by thermal oxidation of PDMS chains during calcination under air. The selective, preferential interaction between TTIP and the hydrophilic POEM chains was responsible for the formation of well-organized TiO2/SiO2 films, as supported by transmission electron microscopy, scanning electron microscopy, X-ray photospectroscopy, and X-ray diffraction analyses. We investigated in detail the effect of precursor content, solvent type, and polymer concentration on thin film morphology. Photodegradation of methyl orange by the well-organized meso-macroporous TiO2/SiO2 film was greater than that of a dense TiO2 film prepared without PDMS-g-POEM as well as a SiO2-etched TiO2 film. These results indicate that the well-organized structure and SiO2 doping of the TiO2 film play a pivotal role in enhancing its photocatalytic properties.

  14. Synthesis of mesoporous TiO2/SiO2 hybrid films as an efficient photocatalyst by polymeric micelle assembly.

    PubMed

    Li, Yunqi; Bastakoti, Bishnu Prasad; Imura, Masataka; Hwang, Soo Min; Sun, Ziqi; Kim, Jung Ho; Dou, Shi Xue; Yamauchi, Yusuke

    2014-05-12

    Thermally stable mesoporous TiO2/SiO2 hybrid films with pore size of 50 nm have been synthesized by adopting the polymeric micelle-assembly method. A triblock copolymer, poly(styrene-b-2-vinyl pyridine-b-ethylene oxide), which serves as a template for the mesopores, was utilized to form polymeric micelles. The effective interaction of titanium tetraisopropoxide (TTIP) and tetraethyl orthosilicate (TEOS) with the polymeric micelles enabled us to fabricate stable mesoporous films. By changing the molar ratio of TEOS and TTIP, several mesoporous TiO2/SiO2 hybrid films with different compositions can be synthesized. The presence of amorphous SiO2 phase effectively retards the growth of anatase TiO2 crystal in the pore walls and retains the original mesoporous structure, even at higher temperature (650 °C). These TiO2/SiO2 hybrid films are of very high quality, without any cracks or voids. The addition of SiO2 phase to mesoporous TiO2 films not only adsorbs more organic dyes, but also significantly enhances the photocatalytic activity compared to mesoporous pure TiO2 film without SiO2 phase.

  15. Incorporation and thermal evolution of rhodamine 6G dye molecules adsorbed in porous columnar optical SiO2 thin films.

    PubMed

    Sánchez-Valencia, Juan R; Blaszczyk-Lezak, Iwona; Espinós, Juan P; Hamad, Said; González-Elipe, Agustín R; Barranco, Angel

    2009-08-18

    Rhodamine 6G (Rh6G) dye molecules have been incorporated into transparent and porous SiO2 thin films prepared by evaporation at glancing angles. The porosity of these films has been assessed by analyzing their water adsorption isotherms measured for the films deposited on a quartz crystal monitor. Composite Rh6G/SiO2 thin films were prepared by immersion of a SiO2 thin film into a solution of the dye at a given pH. It is found that the amount of Rh6G molecules incorporated into the film is directly dependent on the pH of the solution and can be accounted for by a model based on the point of zero charge (PZC) concepts originally developed for colloidal oxides. At low pHs, the dye molecules incorporate in the form of monomers, while dimers or higher aggregates are formed if the pH increases. Depending on the actual preparation and treatment conditions, they also exhibit high relative fluorescence efficiency. The thermal stability of the composite films has been also investigated by characterizing their optical behavior after heating in an Ar atmosphere at increasing temperatures up to 275 degrees C. Heating induces a progressive loss of active dye molecules, a change in their agglomeration state, and an increment in their relative fluorescence efficiency. The obtained Rh6G/SiO2 composite thin films did not disperse the light and therefore can be used for integration into optical and photonic devices.

  16. Nanosecond pulsed laser damage characteristics of HfO2/SiO2 high reflection coatings irradiated from crystal-film interface.

    PubMed

    Cheng, Xinbin; Jiao, Hongfei; Lu, Jiangtao; Ma, Bin; Wang, Zhanshan

    2013-06-17

    The nano-precursors in the subsurface of Nd:YLF crystal were limiting factor that decreased the laser-induced damage threshold (LIDT) of HfO(2)/SiO(2) high reflection (HR) coatings irradiated from crystal-film interface. To investigate the contribution of electric-field (E-field) to laser damage originating from nano-precursors and then to probe the distribution of vulnerable nano-precursors in the direction of subsurface depth, two 1064 nm HfO(2)/SiO(2) HR coatings having different standing-wave (SW) E-field distributions in subsurface of Nd:YLF c5424181043036123rystal were designed and prepared. Artificial gold nano-particles were implanted into the crystal-film interface prior to deposition of HR coatings to study the damage behaviors in a more reliable way. The damage test results revealed that the SW E-field rather than the travelling-wave (TW) E-field contributed to laser damage. By comparing the SW E-field distributions and LIDTs of two HR coating designs, the most vulnerable nano-precursors were determined to be concentrated in a thin redeposition layer that is within 100 nm from the crystal-film interface.

  17. The role of film interfaces in near-ultraviolet absorption and pulsed-laser damage in ion-beam-sputtered coatings based on HfO2/SiO2 thin-film pairs

    DOE PAGES

    Ristau, Detlev; Papernov, S.; Kozlov, A. A.; ...

    2015-11-23

    The role of thin-film interfaces in the near-ultraviolet absorption and pulsed-laser–induced damage was studied for ion-beam–sputtered and electron-beam–evaporated coatings comprised from HfO2 and SiO2 thin-film pairs. To separate contributions from the bulk of the film and from interfacial areas, absorption and damage-threshold measurements were performed for a one-wave (355-nm wavelength) thick, HfO2 single-layer film and for a film containing seven narrow HfO2 layers separated by SiO2 layers. The seven-layer film was designed to have a total optical thickness of HfO2 layers, equal to one wave at 355 nm and an E-field peak and average intensity similar to a single-layer HfO2more » film. Absorption in both types of films was measured using laser calorimetry and photothermal heterodyne imaging. The results showed a small contribution to total absorption from thin-film interfaces, as compared to HfO2 film material. The relevance of obtained absorption data to coating near-ultraviolet, nanosecond-pulse laser damage was verified by measuring the damage threshold and characterizing damage morphology. The results of this study revealed a higher damage resistance in the seven-layer coating as compared to the single-layer HfO2 film in both sputtered and evaporated coatings. Here, the results are explained through the similarity of interfacial film structure with structure formed during the co-deposition of HfO2 and SiO2 materials.« less

  18. Sol-gel SiO2 film contained Au/SiO2/quantum dot core/shell/shell nanostructures with plasmonic enhanced photoluminescence.

    PubMed

    Yang, Ping; Zhang, Lipeng; Wang, Yingzi

    2012-12-01

    A sol-gel method has been developed to fabricate functional silica film with Au/SiO2/quantum dot (QD) core/shell/shell nanostructures which exhibited plasmonic enhanced photoluminescence (PL). Au nanoparticles (NPs) were homogeneously coated with a SiO2 shell by an optimal Stöber synthesis. Hydrophobic CdSe/ZnS QDs was transferred into water phase via a ligand exchange by a thin functional SiO2 layer consisted of partially hydrolyzed 3-aminopropyltrimethoxysilane (APS) sol. The Au/SiO2/QD core/shell/shell nanostructure was created by assembling the functional SiO2-coated QDs to the SiO2-coated Au NPs while QDs transferred into water phase. Those partially hydrolyzed APS molecules play an important role for the connection between the QDs and SiO2-coated Au NPs. The Au/SiO2/QD core/shell/shell nanostructures were embedded in functional sol-gel SiO2 films fabricated via spinning and dipping coating, in which the film revealed strong surface plasmon scattering and enhanced PL. Because of the dual functionality, the film is utilizable for various applications including biological and medical sensors, optical devices, and solar cells. This technique can serve as a general route for encapsulating a variety of nanomaterials in sol-gel films.

  19. Patterned ion beam implantation of Co ions into a SiO2 thin film via ordered nanoporous alumina masks.

    PubMed

    Guan, Wei; Ghatak, Jay; Peng, Yong; Peng, Nianhua; Jeynes, Chris; Inkson, Beverley; Möbus, Günter

    2012-02-03

    Spatially patterned ion beam implantation of 190 keV Co(+) ions into a SiO(2) thin film on a Si substrate has been achieved by using nanoporous anodic aluminum oxide with a pore diameter of 125 nm as a mask. The successful synthesis of periodic embedded Co regions using pattern transfer is demonstrated for the first time using cross-sectional (scanning) transmission electron microscopy (TEM) in combination with analytical TEM. Implanted Co regions are found at the correct relative lateral periodicity given by the mask and at a depth of about 120 nm.

  20. Nonlinear optical performance of poled liquid crystalline azo-dyes confined in SiO2 sonogel films

    NASA Astrophysics Data System (ADS)

    Torres-Zúñiga, V.; Morales-Saavedra, O. G.; Rivera, E.; Flores-Flores, J. O.; Bañuelos, J. G.; Ortega-Martínez, R.

    2010-01-01

    The catalyst-free sonogel route was implemented to fabricate highly pure, optically active, hybrid azo-dye/SiO2-based spin-coated thin films deposited onto ITO-covered glass substrates. The implemented azo-dyes exhibit a push-pull structure; thus chromophore electrical poling was performed in order to explore their quadratic nonlinear optical (NLO) performance and the role of the SiO2 matrix for allowing molecular alignment within the sonogel host network. Morphological and optical characterizations were performed to the film samples according to atomic force microscopy (AFM), ultraviolet-visible (UV-Vis) spectroscopy and the Maker-fringe technique. Regardless of absence of a high glass transition temperature (T g) in the studied monomeric liquid crystalline azo-dyes, some hybrid films displayed stable NLO activity such as second harmonic generation (SHG). Results show that the chromophores were homogeneously embedded within the SiO2 sonogel network, where the guest-host molecular and mechanical interactions permitted a stable monomeric electrical alignment in this kind of environment.

  1. Characterization of local dielectric breakdown in ultrathin SiO2 films using scanning tunneling microscopy and spectroscopy

    NASA Astrophysics Data System (ADS)

    Watanabe, Heiji; Baba, Toshio; Ichikawa, Masakazu

    1999-05-01

    Local dielectric breakdown of ultrathin SiO2 films grown on silicon substrates has been investigated by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). We found that STM observation can reveal individual quasibreakdown spots created by hot-electron injection into the oxide, as well as features of the topography such as atomic steps on the oxide surface. STS was used to study the local electrical properties of the oxide films before and after electrical stressing. We observed a leakage current at the quasibreakdown spots that passed through defect levels in the ultrathin oxide films. We also found that several tunneling spectra obtained from near leakage sites showed clear negative differential resistance. This phenomenon was attributed to the conductance change in the leakage path due to electron charging effects. Moreover, we confirmed the stressing polarity dependence of the leakage-site creation, and that atomic steps on the oxide and at the SiO2/Si interface did not cause any serous problem in the quasibreakdown process.

  2. Sol–gel synthesis and photoluminescence of SiO2–Si:Er3+ nanocomposite films

    NASA Astrophysics Data System (ADS)

    Tuan, P. V.; Khiem, T. N.; Huy, P. T.

    2017-03-01

    In this work, we report on sol–gel synthesis and photoluminescence of SiO2–Si:Er3+ nanocomoposite films. The films were characterized by x-ray diffraction, field emission scanning electron microscope and photoluminescence measurements. We demonstrate that the incorporation of Si nanocrystals with sizes of 10–20 nm into the silica matrix resulted in strong Er-related PL in the infrared region peaking at 1535 nm and that the film can be well excited by non-resonant wavelengths (250–260 nm). The role of Si nanocrystals as sensitizers and the dependence of the Er-related PL on Er-doping concentration and annealing temperature are also discussed.

  3. Ionic liquid versus SiO2 gated a-IGZO thin film transistors: A direct comparison

    DOE PAGES

    Pudasaini, Pushpa Raj; Noh, Joo Hyon; Wong, Anthony T.; ...

    2015-08-12

    Here, ionic liquid gated field effect transistors have been extensively studied due to their low operation voltage, ease of processing and the realization of high electric fields at low bias voltages. Here, we report ionic liquid (IL) gated thin film transistors (TFTs) based on amorphous Indium Gallium Zinc Oxide (a-IGZO) active layers and directly compare the characteristics with a standard SiO2 gated device. The transport measurements of the top IL gated device revealed the n-channel property of the IGZO thin film with a current ON/OFF ratio ~105, a promising field effect mobility of 14.20 cm2V–1s–1, and a threshold voltage ofmore » 0.5 V. Comparable measurements on the bottom SiO2 gate insulator revealed a current ON/OFF ratio >108, a field effect mobility of 13.89 cm2V–1s–1 and a threshold voltage of 2.5 V. Furthermore, temperature-dependent measurements revealed that the ionic liquid electric double layer can be “frozen-in” by cooling below the glass transition temperature with an applied electrical bias. Positive and negative freezing bias locks-in the IGZO TFT “ON” and “OFF” state, respectively, which could lead to new switching and possibly non-volatile memory applications.« less

  4. Nanoscale control of Si nanoparticles within a 2D hexagonal array embedded in SiO2 thin films

    NASA Astrophysics Data System (ADS)

    Castro, Celia; BenAssayag, Gérard; Pecassou, Béatrice; Andreozzi, Andrea; Seguini, Gabriele; Perego, Michele; Schamm-Chardon, Sylvie

    2017-01-01

    In this work, we investigate the ability to control Si nanoparticles (NPs) spatially arranged in a hexagonal network of 20 nm wide nanovolumes at controlled depth within SiO2 thin films. To achieve this goal an unconventional lithographic technique was implemented based on a bottom-up approach, that is fully compatible with the existing semiconductor technology. The method combines ultra-low energy ion beam synthesis with nanostructured block-copolymer thin films that are self-assembled on the SiO2 substrates to form a nanoporous template with hexagonally packed pores. A systematic analytical investigation using time of flight-secondary ion mass spectroscopy and low-loss energy filtered transmission electron microscopy demonstrates that by adjusting few fabrication parameters, it is possible to narrow the size distribution of the NPs and to control the number of NPs per nanovolume. Experimental results are critically discussed on the basis of literature data, providing a description of the mechanism involved in the formation of Si NPs.

  5. CONDENSED MATTER: STRUCTURE, MECHANICAL AND THERMAL PROPERTIES: Tunable Anisotropic Absorption of Ag-Embedded SiO2 Thin Films by Oblique Angle Deposition

    NASA Astrophysics Data System (ADS)

    Xiao, Xiu-Di; Dong, Guo-Ping; Shao, Jian-Da; Fan, Zheng-Xiu; He, Hong-Bo; Qi, Hong-Ji

    2009-08-01

    Ag-embedded SiO2 thin films are prepared by oblique angle deposition. Through field emission scanning electron microscopy (SEM), an orientated slanted columnar structure is observed. Energy-dispersive x-ray (EDX) analysis shows the Ag concentration is about 3% in the anisotropic SiO2 matrix. Anisotropic surface plasma resonance (SPR) absorption is observed in the Ag-embedded SiO2 thin films, which is dependent on polarization state and incidence angle of two orthogonal polarized lights and the deposition angle. This means that optical properties and anisotropic SPR absorption can be tunable in Ag-embedded SiO2 thin films. Broadband polarization splitting is also observed and the transmission ratio Tp/Ts between p- and s-polarized lights is up to 2.7 for thin films deposited at α = 70°, which means that Ag-embedded SiO2 thin films are a promising candidate for thin film polarizers.

  6. Spin-Relaxation Dynamics of E' Centers at High Density in SiO2 Thin Films for Single-Spin Tunneling Force Microscopy

    NASA Astrophysics Data System (ADS)

    Ambal, K.; Payne, A.; Waters, D. P.; Williams, C. C.; Boehme, C.

    2015-08-01

    The suitability of the spin dynamics of paramagnetic silicon dangling bonds (E' centers) in high-E'-density amorphous silicon dioxide (SiO2 ) as probe spins for single-spin tunneling force microscopy (SSTFM) is studied. SSTFM is a spin-selection-rule-based scanning-probe single-spin readout concept. Following the synthesis of SiO2 thin films on (111)-oriented crystalline-silicon substrates with room-temperature stable densities of [E'] >5 ×1018 cm-3 throughout the 60-nm thin film, pulsed electron paramagnetic resonance spectroscopy is conducted on the E' centers at temperatures between T =5 K and T =70 K . The measurements reveal that the spin coherence (the transverse spin-relaxation time T2) of these centers is significantly shortened compared to low-E'-density SiO2 films and within error margins not dependent on temperature. In contrast, the spin-flip times (the longitudinal relaxation times T1) are dependent on the temperature but with much weaker dependence than low-density SiO2 , with the greatest deviations from low-density SiO2 seen for T =5 K . These results, discussed in the context of the spin-relaxation dynamics of dangling-bond states of other silicon-based disordered solids, indicate the suitability of E' centers in high-density SiO2 as probe spins for SSTFM.

  7. A polycrystalline SiO2 colloidal crystal film with ultra-narrow reflections.

    PubMed

    Fu, Qianqian; Chen, Ang; Shi, Lei; Ge, Jianping

    2015-04-30

    This work reported a high quality photonic crystal film with an ultra-narrow photonic bandgap obtained via a chemical synthetic route. The bandgap is much narrower than that of traditional colloidal crystals, which makes the film qualified for use in optical devices. The narrow PBG originates from not only the high crystallinity and uniform orientations of microcrystals within the film but also the very close refractive indices between the silica and the polymer matrix. Due to the matching of the refractive index, the amorphous contents of the film are optically transparent and do not interfere with the reflection, so that the photonic crystal film is tolerant of the existence of disordered contents.

  8. Sol-gel preparation and characterization of SiO2 coated VO2 films with enhanced transmittance and high thermochromic performance

    NASA Astrophysics Data System (ADS)

    Li, Dezeng; Shan, Yongkui; Huang, Fuqiang; Ding, Shangjun

    2014-10-01

    Vanadium dioxide (VO2) films prepared at low-temperature with a low cost are considerable for energy-saving applications. Here, SiO2 coated VO2 films with clearly enhanced visible transmittance by introducing antireflection coatings (ARCs) and excellent thermochromic performance were present. The VO2 films have been prepared via a stable and low-cost sol-gel synthesis route using vanadium pentaoxide powder as precursor, and their structural, morphological, optical and electrical properties and thermochromic performance were systemically characterized. The resistance of VO2 films varies by 4 orders of magnitude and the transmittance changes from 11.8% to 69.3% at 2500 nm while no significant deviation appears in the visible region during metal-insulator transition (MIT). Nanoporous SiO2 coating with good optical transparency was coated on the surface of VO2 film via sol-gel dip-coating technique to enhance its optical transmittance, and the visible transmittance is increased by 14.6% due to the significantly decreased reflectance. The critical transition temperature (63 °C) and infrared switching properties of VO2 films are not much deteriorated by applying SiO2 layer. The synergistic effect of antireflection and thermochromism on SiO2 coated VO2 films was investigated.

  9. Luminescence of Eu(3+) doped SiO2 Thin Films and Glass Prepared by Sol-gel Technology

    NASA Technical Reports Server (NTRS)

    Castro, Lymari; Jia, Weiyi; Wang, Yanyun; Santiago, Miguel; Liu, Huimin

    1998-01-01

    Trivalent europium ions are an important luminophore for lighting and display. The emission of (5)D0 to (7)F2 transition exhibits a red color at about 610 nm, which is very attractive and fulfills the requirement for most red-emitting phosphors including lamp and cathode ray phosphorescence materials. Various EU(3+) doped phosphors have been developed, and luminescence properties have been extensively studied. On the other hand, sol-gel technology has been well developed by chemists. In recent years, applications of this technology to optical materials have drawn a great attention. Sol-gel technology provides a unique way to obtain homogeneous composition distribution and uniform doping, and the processing temperature can be very low. In this work, EU(3+) doped SiO2 thin films and glasses were prepared by sol-gel technology and their spectroscopic properties were investigated.

  10. Infrared interference coating by use of Si3N4 and SiO2 films with ion-assisted deposition.

    PubMed

    Lee, Cheng-Chung; Ku, Shih-Liang

    2010-01-20

    Silicon nitride (Si(3)N(4)) and silicon dioxide (SiO(2)) films were prepared by ion-assisted deposition, and a higher deposition rate was achieved for both films. The results of x-ray diffraction and transmission electron microscopy measurements showed that the films have amorphous structures. As measured by infrared (IR) spectrometry and x-ray photoelectron spectrometry, both stoichiometric films have extremely low hydrogen content. The IR optical constants of the films were determined by spectroscopic ellipsometry. Both films exhibited a low extinction coefficient at wavelengths from 2 to 7 microm. The application of Si(3)N(4) and SiO(2) films on the IR interference coating is demonstrated.

  11. A sandwich structured SiO(2)/cytochrome c/SiO(2) on a boron-doped diamond film electrode as an electrochemical nitrite biosensor.

    PubMed

    Geng, Rong; Zhao, Guohua; Liu, Meichuan; Li, Mingfang

    2008-06-01

    A novel sandwich structured SiO(2) gel/cytochrome c (Cyt c)/SiO(2) gel was designed and constructed on conductive boron-doped diamond (BDD) film substrate. A SiO(2) gel membrane was first in situ deposited on the pretreated positive charged H-terminated BDD electrode with a simple and artful surface vapor sol-gel method. Cyt c was subsequently immobilized onto the SiO(2) membranes by electrostatic attraction, followed by another SiO(2) gel layer in situ depositing on it. The SiO(2) interlayer was conceived to play an important role in the resultant sandwich structured SiO(2)/Cyt c/SiO(2)/BDD electrode as a selective "semi-open" medium, which guaranteed the immobilized Cyt c to maintain high stability and perform good electrochemistry and biocatalysis responses. The bioactivity of Cyt c was well protected and the immobilized biomolecule even didn't denature at extremely high or low pH condition. More attractively, Cyt c in the sandwich structured electrode could be further oxidized into highly reactive Cyt c pi-cation by two-step electrochemical oxidation, which could oxidize NO(2)(-) into NO(3)(-) in the solution. A sensitive determination approach of nitrite was accordingly built up based on this biocatalytic oxidative interaction for the first time and a possible mechanism of the interaction was herein proposed.

  12. Nature of point defects on SiO2/Mo(112) thin films and their interaction with Au atoms.

    PubMed

    Martinez, Umberto; Giordano, Livia; Pacchioni, Gianfranco

    2006-08-31

    We have studied by means of periodic DFT calculations the structure and properties of point defects at the surface of ultrathin silica films epitaxially grown on Mo(112) and their interaction with adsorbed Au atoms. For comparison, the same defects have been generated on an unsupported silica film with the same structure. Four defects have been considered: nonbridging oxygen (NBO, [triple bond]Si-O(*)), Si dangling bond (E' center, [triple bond]Si(*)), oxygen vacancy (V(O), [triple bond]Si-Si[triple bond]), and peroxo group ([triple bond]Si-O-O-Si[triple bond]), but only the NBO and the V(O) centers are likely to form on the SiO(2)/Mo(112) films under normal experimental conditions. The [triple bond]Si-O(*) center captures one electron from Mo forming a silanolate group, [triple bond]Si-O(-), sign of a direct interaction with the metal substrate. Apart from the peroxo group, which is unreactive, the other defects bind strongly the Au atom forming stable surface complexes, but their behavior may differ from that of the same centers generated on an unsupported silica film. This is true in particular for the two most likely defects considered, the nonbridging oxygen, [triple bond]Si-O(*), and the oxygen vacancy, [triple bond]Si-Si[triple bond].

  13. Nonlinear optical absorption and switching properties of gold nanoparticle doped SiO2-TiO2 sol-gel films.

    PubMed

    Venkatram, N; Kumar, R Sai Santosh; Rao, D Narayana; Medda, S K; De, Sucheta; De, Goutam

    2006-07-01

    The nonlinear optical absorption and switching properties of sol-gel derived of Au nanoparticle doped SiO2-TiO2 sol-gel films having different Au-surface plasmon absorption positions are reported in this paper. The Au nanoparticles are embedded in SiO2 and SiO2-TiO2 mixed glassy film matrices with different refractive index values. To study the nonlinear absorption properties, lasers with three different wavelengths are used. The optical switching behavior is studied by using the pump-probe technique with 532 nm as the excitation wavelength. Ground state conduction band, surface plasmon band, and the free carrier band are taken as three level model to explain theoretically the obtained RSA and SA behaviors.

  14. Optical, electrical and dielectric properties of TiO2-SiO2 films prepared by a cost effective sol-gel process.

    PubMed

    Vishwas, M; Rao, K Narasimha; Gowda, K V Arjuna; Chakradhar, R P S

    2011-12-01

    Titanium dioxide (TiO(2)) and silicon dioxide (SiO(2)) thin films and their mixed films were synthesized by the sol-gel spin coating method using titanium tetra isopropoxide (TTIP) and tetra ethyl ortho silicate (TEOS) as the precursor materials for TiO(2) and SiO(2) respectively. The pure and composite films of TiO(2) and SiO(2) were deposited on glass and silicon substrates. The optical properties were studied for different compositions of TiO(2) and SiO(2) sols and the refractive index and optical band gap energies were estimated. MOS capacitors were fabricated using TiO(2) films on p-silicon (100) substrates. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were studied and the electrical resistivity and dielectric constant were estimated for the films annealed at 200°C for their possible use in optoelectronic applications.

  15. Optical, electrical and dielectric properties of TiO 2-SiO 2 films prepared by a cost effective sol-gel process

    NASA Astrophysics Data System (ADS)

    Vishwas, M.; Rao, K. Narasimha; Gowda, K. V. Arjuna; Chakradhar, R. P. S.

    2011-12-01

    Titanium dioxide (TiO 2) and silicon dioxide (SiO 2) thin films and their mixed films were synthesized by the sol-gel spin coating method using titanium tetra isopropoxide (TTIP) and tetra ethyl ortho silicate (TEOS) as the precursor materials for TiO 2 and SiO 2 respectively. The pure and composite films of TiO 2 and SiO 2 were deposited on glass and silicon substrates. The optical properties were studied for different compositions of TiO 2 and SiO 2 sols and the refractive index and optical band gap energies were estimated. MOS capacitors were fabricated using TiO 2 films on p-silicon (1 0 0) substrates. The current-voltage ( I- V) and capacitance-voltage ( C- V) characteristics were studied and the electrical resistivity and dielectric constant were estimated for the films annealed at 200 °C for their possible use in optoelectronic applications.

  16. Investigation of solar cell performance using multilayer thin film structure (SiO2/Si3N4) and grating

    NASA Astrophysics Data System (ADS)

    Dubey, R. S.; Jhansirani, K.; Singh, Shyam

    Thin film silicon solar cells are the better choice due to their low cost as compared to the crystalline solar cells. However, thin film silicon solar cells are suffering from a problem of weak absorption of incident light and hence, light trapping mechanism is essential for the harvesting of maximum solar radiation. In this paper, we present the performance of solar cell using an efficient back reflector composed of multilayer thin film (SiO2/Si3N4) and a diffraction grating. The use of a back reflector showed enhanced light absorption due to the folding of unabsorbed light coming to it after crossing the active region in a wide wavelength range. Further, the effect of active layer thickness and grating height were also discussed for the optimal performance of the solar cell. In the case of magnetic transverse mode, a relative enhancement in cell efficiency about 79 and 21% respectively have been observed with respect to a planar and SC4 solar cells.

  17. Polymeric fibre optic sensor based on a SiO2 nanoparticle film for humidity sensing on wounds

    NASA Astrophysics Data System (ADS)

    Gomez, David; Morgan, Stephen P.; Hayes Gill, Barrie R.; Korposh, Serhiy

    2016-05-01

    Optical fibre sensors have the potential to be incorporated into wound dressings to monitor moisture and predict healing without the need to remove the dressing. A low cost polymeric optical fibre humidity sensor based on evanescent wave absorption is demonstrated for skin humidity measurement. The sensor is fabricated by coating the fibre with a hydrophilic film based on bilayers of Poly(allylamine hydrochloride) (PAH) and SiO2 mesoporous nanoparticles. The Layer-by-Layer method was used for the deposition of the layers. Multimode polymeric optical fibre with a cladding diameter of 250μm was covered by 7 layers of PAH/SiO2 film on the central region of an unclad fibre with a diameter of 190μm. The length of the sensitive region is 30mm. Experiment results show a decrease in light intensity when relative humidity increases due to refractive index changes of the fibre coating. The sensitivity obtained was 200mV/%RH and the sensor was demonstrated to provide a faster response to changes in the humidity of the skin microenvironment than a commercial sensor.

  18. Effect of Cations on the Chemical Mechanical Polishing of SiO2 Film

    NASA Astrophysics Data System (ADS)

    Song, Han; Wang, Liang-Yong; Liu, Wei-Li; Song, Zhi-Tang

    2013-09-01

    We investigate the effect of cations with different valences on the chemical mechanical polishing (CMP) of silicon dioxide films. The removal rate and surface roughness of the silicon-dioxide-film post-CMP are checked for the silica-based slurry with different cation salts (NaCl, CaCl2, AlCl3). Meanwhile, the particle size and size distribution of the slurries are characterized to test their lifetimes. The result shows that the three kinds of salts can improve the polishing removal rate from around 20 nm/min to 120 nm/min without affecting the surface roughness when the polishing slurry is stable. With increasing valence of cations, the polishing slurry requires less cation concentration to be added to improve the removal rate, while keeping a superior surface topography and maintaining a longer lifetime as well.

  19. Synthesis of CeO2@SiO2 core-shell nanoparticles by water-in-oil microemulsion. Preparation of functional thin film.

    PubMed

    Grasset, F; Marchand, R; Marie, A-M; Fauchadour, D; Fajardie, F

    2006-07-15

    Synthesis of nanoparticles under restricted environment offered by water-in-oil (W/O) microemulsions provides excellent control over particle size and shape, and inter-particle spacing. Such an environment has been involved to synthesize silica nanoparticles with a CeO2 core, so-called CeO2@SiO2. Aqueous fluids made up of ceria nanoparticles with a size close to 5 nm have been used as the water phase component. The starting CeO2 sols and obtained CeO2@SiO2 nanoparticles have been characterized by dynamic light scattering (DLS), X-ray diffraction, scanning and transmission electron microscopy, and specific surface area measurements. The microemulsion process has been characterized by DLS. Preliminary results on CeO2@SiO2 thin films are presented.

  20. Molecular dynamics simulations of dotriacontane films supported on a SiO2 surface

    NASA Astrophysics Data System (ADS)

    Gutierrez, Sebastian; Araya, Raul; Perez-Acle, Tomas; Retamal, Maria Jose; Volkmann, Ulrich G.

    2011-03-01

    Dotriacontane (C32 H66 , C32) films supported on Si O2 surfaces were studied using very high-resolution ellipsometry, atomic force microscopy (AFM) and x-ray reflectivity techniques. For almost complete layers a model was proposed in which the C32/ Si O2 interfacial region is characterized by a parallel bilayer and perpendicular layers on top. Recent AFM measurements performed on samples forming sea-weed like structures, showed that for these particular perpendicular ``fractal like'' layers the heights are lower than the all-trans length of dotriacontane (42.5 AA). To gain insights on the internal molecular ordering and layering of C32 supported on Si O2 surfaces, we used all-atom molecular dynamics to simulate C32 films at different temperatures. Our results confirm the presence of the parallel bilayer suggesting the existence of a mixed layer on top, formed by molecules with both parallel and perpendicular segments. These findings suggest a different molecular architecture for sea-weed like structures of dotriacontane supported on Si O2 .

  1. Purely electronic switching with high uniformity, resistance tunability, and good retention in Pt-dispersed SiO2 thin films for ReRAM.

    PubMed

    Choi, Byung Joon; Chen, Albert B K; Yang, Xiang; Chen, I-Wei

    2011-09-01

    Resistance switching memory operating by a purely electronic switching mechanism, which was first realized in Pt-dispersed SiO2 thin films, satisfies criteria including high uniformity, fast switching speed, and long retention for non-volatile memory application. This resistive element obeys Ohm's law for the area dependence, but its resistance exponentially increases with the film thickness, which provides new freedom to tailor the device characteristics.

  2. Comparison of the annealing behavior of thin Ta films deposited onto Si and SiO2 substrates.

    PubMed

    Hübner, R; Hecker, M; Mattern, N; Hoffmann, V; Wetzig, K; Engelmann, H-J; Zschech, E

    2004-06-01

    Structural changes at annealing temperatures (T(an)) of 500-1,100 degrees C were investigated for thin Ta films which were sputter-deposited onto pure Si substrates and onto thermally oxidized Si. In the as-deposited state, the Ta layers predominantly consist of metastable tetragonal beta-Ta, whereby the [001] texture is independent of the substrate material. At lower annealing temperatures, the microstructural evolution is essentially the same for both Ta films. Incorporation of O atoms causes an increase of the intrinsic compressive stress, and diffusion of C atoms into the Ta layer leads to the formation of Ta(2)C. Additionally, a partial transformation of the original beta-Ta phase into a second phase with tetragonal unit cell (denoted as beta'-Ta) occurs. For the Ta/Si system, the formation of a Ta-Si intermixing layer is initiated at T(an)=550 degrees C, and nucleation of crystalline TaSi(2) occurs at T(an)=620 degrees C. The formation of a second Ta silicide was not detected up to T(an)=900 degrees C. In the case of the Ta film deposited onto the SiO(2) substrate, the metastable beta-Ta and the beta'-Ta transform completely into the thermodynamically stable cubic alpha-Ta at T(an)=750 degrees C. A marked reaction with the substrate indicated by the formation of Ta(2)O(5) and Ta(5)Si(3) occurs at T(an)=1,000 degrees C.

  3. Film growth, adsorption and desorption kinetics of indigo on SiO2

    PubMed Central

    Scherwitzl, Boris; Resel, Roland; Winkler, Adolf

    2015-01-01

    Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer des orption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption. PMID:24832297

  4. Film growth, adsorption and desorption kinetics of indigo on SiO2.

    PubMed

    Scherwitzl, Boris; Resel, Roland; Winkler, Adolf

    2014-05-14

    Organic dyes have recently been discovered as promising semiconducting materials, attributable to the formation of hydrogen bonds. In this work, the adsorption and desorption behavior, as well as thin film growth was studied in detail for indigo molecules on silicon dioxide with different substrate treatments. The material was evaporated onto the substrate by means of physical vapor deposition under ultra-high vacuum conditions and was subsequently studied by Thermal Desorption Spectroscopy (TDS), Auger Electron Spectroscopy, X-Ray Diffraction, and Atomic Force Microscopy. TDS revealed initially adsorbed molecules to be strongly bonded on a sputter cleaned surface. After further deposition a formation of dimers is suggested, which de-stabilizes the bonding mechanism to the substrate and leads to a weakly bonded adsorbate. The dimers are highly mobile on the surface until they get incorporated into energetically favourable three-dimensional islands in a dewetting process. The stronger bonding of molecules within those islands could be shown by a higher desorption temperature. On a carbon contaminated surface no strongly bonded molecules appeared initially, weakly bonded monomers rather rearrange into islands at a surface coverage that is equivalent to one third of a monolayer of flat-lying molecules. The sticking coefficient was found to be unity on both substrates. The desorption energies from carbon covered silicon dioxide calculated to 1.67 ± 0.05 eV for multilayer desorption from the islands and 0.84 ± 0.05 eV for monolayer desorption. Corresponding values for desorption from a sputter cleaned surface are 1.53 ± 0.05 eV for multilayer and 0.83 ± 0.05 eV for monolayer desorption.

  5. Adsorption and self-assembly of M13 phage into directionally organized structures on C and SiO2 films.

    PubMed

    Moghimian, Pouya; Srot, Vesna; Rothenstein, Dirk; Facey, Sandra J; Harnau, Ludger; Hauer, Bernhard; Bill, Joachim; van Aken, Peter A

    2014-09-30

    A versatile method for the directional assembly of M13 phage using amorphous carbon and SiO2 thin films was demonstrated. A high affinity of the M13 phage macromolecules for incorporation into aligned structures on an amorphous carbon surface was observed at the concentration range, in which the viral nanofibers tend to disorder. In contrast, the viral particles showed less freedom to adopt an aligned orientation on SiO2 films when deposited in close vicinity. Here an interpretation of the role of the carbon surface in significant enhancement of adsorption and generation of viral arrays with a high orientational order was proposed in terms of surface chemistry and competitive electrostatic interactions. This study suggests the use of amorphous carbon substrates as a template for directional organization of a closely-packed and two-dimensional M13 viral film, which can be a promising route to mineralize a variety of smooth and homogeneous inorganic nanostructure layers.

  6. Ion induced dewetting of Au-Si on a SiO2 surface: composite nanodot evolution and wettability transition.

    PubMed

    Datta, D P; Siva, V; Varma, S; Kanjilal, D; Sahoo, P K

    2016-11-21

    A nanodot array morphology gradually develops on SiO2 surface when a thin bi-layer of Au and Si undergoes ion irradiation. An increasing amount of gold silicide is detected as islands on the insulator surface evolve into nanodots as a function of increasing ion fluence. Different stages of evolution from islands to nanodots are found to be driven by the localized melting of Au along the ion-track and dewetting of the metal film. Dewetting is accompanied by sputter-erosion and mixing of Au and Si at the bi-layer interface due to ion energy deposition. Interestingly, a gradual transition in wettability of the surface from the hydrophilic to the hydrophobic one is observed with the growth of nanodots, which is correlated with the compositional variation. The experimental results indicate a route towards the controlled growth of composite nanodots on an insulator surface having hydrophobic properties using ion irradiation.

  7. Frictional characteristics of nano-scale mesoporous SiO2 thin film formed by sol-gel and self-assembly method.

    PubMed

    Lee, Gyu-Sun; Shin, Yun-Ha; Kim, Ji-Man; Kim, Tae-Sung; Lee, Young-Ze

    2009-12-01

    The pores on the surface function as an outlet for wear particles and enhance the storage of lubricants, which improves lubrication effectiveness. Mesoporous SiO2 thin films were formed by the sol-gel and self-assembly methods to have a porous structure. One of the important issues in the manufacturing of the films involves the control of the porous structure to ensure proper mechanical properties. Mesoporous materials were manufactured with two surfactants, Pluronid Polyol (F127) and Cetyltrimethylammonium Bromide (CTABr). The pores were then exposed on the surface by chemical mechanical polishing (CMP) and plasma-etching. Ball-on-disk tests with mesoporous SiO2 thin films on glass specimens were conducted. The results show that the friction coefficient and wear volume of a specimen with F127, which has a 8 nm pore size, are far lower than those of CTABr, which has a 3 nm pore size at both the dry condition and at boundary lubricated condition. This proves a significant dependency of friction and wear on pore size of mesoporous SiO2 thin films.

  8. Enhanced germanium precipitation and nanocrystal growth in the Ge+ ion-implanted SiO2 films during high-pressure annealing

    NASA Astrophysics Data System (ADS)

    Tyschenko, Ida E.; Volodin, Vladimir A.; Cherkov, Alexander G.

    2016-12-01

    The effect of pressure employed during subsequent annealing of the Ge+-ion implanted SiO2 layers on the Ge nanocrystal formation was studied. Ge+ ions implanted in the thin SiO2 layers formed Gauss-like profiles with a Ge peak concentration varied from 1 to 12 at%. Subsequent annealing was carried out at temperature 600-1130 °C under pressures 1-1.2×104 bar. Strong effect of the pressure on the Ge atom distribution was obtained. High-temperature annealing under pressure within the range of 1-103 bar resulted in the out-diffusion of germanium from the SiO2 layer to the Si substrate. As the pressure reached 1.2×104 bar, Ge migration to the Si/SiO2 interface was prevented. At that, the Ge nanocrystal growth within the ion-implanted region of the SiO2 film took place. The nanocrystal size was investigated as a function both of the Ge atom concentration and the annealing temperature. The obtained results show a diffusion-controlled nanocrystal growth mechanism. The high-pressure (1.2×104 bar) diffusion coefficient of germanium in silicon dioxide was estimated as a function of the temperature and expressed by D=1.1×10-10 exp(-1.43 eV/kT) cm2/s.

  9. SiO2-nanocomposite film coating of CAD/CAM composite resin blocks improves surface hardness and reduces susceptibility to bacterial adhesion.

    PubMed

    Kamonwanon, Pranithida; Hirose, Nanako; Yamaguchi, Satoshi; Sasaki, Jun-Ichi; Kitagawa, Haruaki; Kitagawa, Ranna; Thaweboon, Sroisiri; Srikhirin, Toemsak; Imazato, Satoshi

    2017-01-31

    Composite resin blocks for computer-aided design/computer-aided manufacturing (CAD/CAM) applications have recently become available. However, CAD/CAM composite resins have lower wear resistance and accumulate more plaque than CAD/CAM ceramic materials. We assessed the effects of SiO2-nanocomposite film coating of four types of CAD/CAM composite resin blocks: Cerasmart, Katana Avencia block, Lava Ultimate, and Block HC on surface hardness and bacterial attachment. All composite blocks with coating demonstrated significantly greater Vickers hardness, reduced surface roughness, and greater hydrophobicity than those without coating. Adhesion of Streptococcus mutans to the coated specimens was significantly less than those for the uncoated specimens. These reduced levels of bacterial adherence on the coated surface were still evident after treatment with saliva. Surface modification by SiO2-nanocomposite film coating has potential to improve wear resistance and susceptibility to plaque accumulation of CAD/CAM composite resin restorations.

  10. Transition from isolated submicrometer pits to integral ablation of HfO2 and SiO2 films under subpicosecond irradiation

    NASA Astrophysics Data System (ADS)

    Wang, Hu; Qi, Hongji; Zhao, Jiaoling; Wang, Bin; Shao, Jianda

    2017-03-01

    Damage behavior of HfO2 and SiO2 films under subpicosecond irradiation is investigated experimentally and theoretically in this work. The typical damage phenomenon is the transition from isolated submicrometer pits to integral ablation at transitive threshold. The experimental damage thresholds for both coatings are consistent with the theoretical calculation. The rate equation considering the feedback effect of electron number density is applied to calculate the deposited energy density, which illustrates the evolution of damage morphology.

  11. Evidence for strain-induced local conductance modulations in single-layer graphene on SiO2.

    PubMed

    Teague, M L; Lai, A P; Velasco, J; Hughes, C R; Beyer, A D; Bockrath, M W; Lau, C N; Yeh, N-C

    2009-07-01

    Graphene has emerged as an electronic material that is promising for device applications and for studying two-dimensional electron gases with relativistic dispersion near two Dirac points. Nonetheless, deviations from Dirac-like spectroscopy have been widely reported with varying interpretations. Here we show evidence for strain-induced spatial modulations in the local conductance of single-layer graphene on SiO(2) substrates from scanning tunneling microscopic (STM) studies. We find that strained graphene exhibits parabolic, U-shaped conductance vs bias voltage spectra rather than the V-shaped spectra expected for Dirac fermions, whereas V-shaped spectra are recovered in regions of relaxed graphene. Strain maps derived from the STM studies further reveal direct correlation with the local tunneling conductance. These results are attributed to a strain-induced frequency increase in the out-of-plane phonon mode that mediates the low-energy inelastic charge tunneling into graphene.

  12. High temperature coefficient of resistance of low-temperature-grown VO2 films on TiO2-buffered SiO2/Si (100) substrates

    NASA Astrophysics Data System (ADS)

    Miyazaki, Kenichi; Shibuya, Keisuke; Suzuki, Megumi; Wado, Hiroyuki; Sawa, Akihito

    2015-08-01

    The introduction of a TiO2 buffer layer significantly improved the temperature coefficient of resistance (TCR), a measure of the sharpness of the metal-insulator transition, for films of VO2 grown on SiO2/Si (100) substrates at growth temperatures below 670 K. X-ray diffraction and Raman scattering measurements revealed that polycrystalline VO2 films were formed on the TiO2-buffered substrates at low temperatures below 600 K, whereas amorphous films were formed at these temperatures on SiO2/Si (100) substrates without a TiO2 buffer layer. Electron microscopy studies confirmed that the TiO2 buffer layer enhanced the grain growth of VO2 films at low growth temperatures. The VO2 films grown at 600 K on TiO2-buffered substrates showed a large TCR of more than 80%/K as a result of the improved crystallinity and grain size of the VO2 films. Our results provide an effective approach toward the integration of VO2-based devices onto Si platforms at process temperatures below 670 K.

  13. The enhanced photocatalytic activity and self-cleaning properties of mesoporous SiO2 coated Cu-Bi2O3 thin films.

    PubMed

    Shan, Wenjie; Hu, Yun; Zheng, Mengmeng; Wei, Chaohai

    2015-04-28

    Mesoporous SiO2 coated Cu-Bi2O3 thin films (meso-SiO2/Cu-Bi2O3) were prepared on glass substrates using a simple sol-gel/spin-coating method. The structure and optical properties were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, a UV-vis spectrophotometer and a water contact angle meter. The photocatalytic activity and self-cleaning properties of the films were investigated through the degradation of methyl orange and stearic acid, respectively. It was found that the meso-SiO2/Cu-Bi2O3 thin films were highly transparent and showed excellent superhydrophilicity even in the dark. The thin films exhibited enhanced photocatalytic activity and self-cleaning properties compared to pure Bi2O3 films, which was attributed to the cooperation of the interfacial charge transfer between Bi2O3 and surface Cu species as well as the unique mesoporous SiO2 structure. The results showed that the films can be used as promising self-cleaning and antifogging materials.

  14. The structural studies of Ag containing TiO2-SiO2 gels and thin films deposited on steel

    NASA Astrophysics Data System (ADS)

    Adamczyk, Anna; Rokita, Magdalena

    2016-06-01

    FTIR spectroscopic structural studies of titania-silica monolith samples as well as thin films deposited on steel were described in this work. Thin films were synthesized by the sol-gel method applying the dip coating as separate one-component TiO2 and/or SiO2 layers or as two-component TiO2-SiO2 thin films. Silver nanoparticles were incorporated into the structure from pure SiO2 sol, deposited then as an additional layer in those hybrid multilayers systems. Except the spectroscopic studies, XRD diffraction, SEM microscopy with EDX analysis and AFM microscopy were applied. The structural studies allow to describe and compare the structure and the morphology of thin films, as well those Ag free as Ag containing ones, also by the comparison with the structure of bulk samples. In FTIR spectra, the band observed at about 613 cm-1 can be connected with the presence of the non-tetrahedral cation in the structure and is observed only in the spectra of Ag containing bulk samples and thin films. The bands at 435-467 cm-1 are due to the stretching vibrations of Ti-O bonds or as well to the bending vibrations of O-Si-O one. In the ranges of 779-799 cm-1 and 1027-1098 cm-1, the bands ascribed to the symmetric stretching vibrations and asymmetric vibrations of Si-O-Si connections, respectively, are observed. SEM and AFM images gave the information on the microstructure and the topography of samples surface. XRD measurements confirmed the presence of only amorphous phase in samples up to 500 °C and allowed to observe the tendency of their crystallization.

  15. SiO2/TiO2/n-Si/Ag(Cr)/TiO2 thin films with superhydrophilicity and low-emissivity

    NASA Astrophysics Data System (ADS)

    Loka, Chadrasekhar; Ryeol Park, Kyoung; Lee, Kee-Sun

    2016-01-01

    In this study, SiO2/TiO2/n-Si/Ag(Cr)/TiO2 multilayer structures have been designed and deposited by the RF and DC magnetron sputtering at room temperature. The as-deposited TiO2/glass films which are initially amorphous in nature were subjected to post annealing at 673 K for anatase phase TiO2. The anatase TiO2 films showed an optical bandgap ˜3.32 eV. The Ag(Cr)/TiO2 showed very low-emissivity (low-e) value ˜0.081 which is evaluated by using the sheet resistance (6.51 Ω/□) of the films. All the deposited films showed high visible transmittance (˜81%) and high infrared reflectance (72%) which are recorded by using the UV-vis-NIR spectrophotometer. In addition, experimentally obtained optical properties were in good agreement with the simulation data. The TiO2/n-Si heterojunction concept has been employed to enhance the superhydrophilicity of the deposited multilayer stack, TiO2/n-Si/Ag(Cr)/TiO2 films exhibited best superhydrophilicity with water contact angle ˜2°. The deposited multilayer structures SiO2/TiO2/n-Si/Ag(Cr)/TiO2 and TiO2/n-Si/Ag(Cr)/TiO2 achieved significant low-e and superhydrophilicity.

  16. Comparison of Ag and SiO2 Nanoparticles for Light Trapping Applications in Silicon Thin Film Solar Cells.

    PubMed

    Theuring, Martin; Wang, Peng Hui; Vehse, Martin; Steenhoff, Volker; von Maydell, Karsten; Agert, Carsten; Brolo, Alexandre G

    2014-10-02

    Plasmonic and photonic light trapping structures can significantly improve the efficiency of solar cells. This work presents an experimental and computational comparison of identically shaped metallic (Ag) and nonmetallic (SiO2) nanoparticles integrated to the back contact of amorphous silicon solar cells. Our results show comparable performance for both samples, suggesting that minor influence arises from the nanoparticle material. Particularly, no additional beneficial effect of the plasmonic features due to metallic nanoparticles could be observed.

  17. Microstructure and optical dispersion characterization of nanocomposite sol-gel TiO2-SiO2 thin films with different compositions

    NASA Astrophysics Data System (ADS)

    Kermadi, S.; Agoudjil, N.; Sali, S.; Zougar, L.; Boumaour, M.; Broch, L.; En Naciri, A.; Placido, F.

    2015-06-01

    Nanocomposite TiO2-SiO2 thin films with different compositions (from 0 to 100 mol% TiO2) were deposited by sol-gel dip-coating method on silicon substrate. Crystal structure, chemical bonding configuration, composition and morphology evolutions with composition were followed by Raman scattering, Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy and scanning electron microscopy respectively. The refractive index and the extinction coefficient were derived in a broad band wavelength (250-900 nm) from spectroscopic ellipsometry data with high accuracy and correlated with composition and microstructure. Results showed an anatase structure for 100% TiO2 with a grain size in 6-10 nm range. Whereas, the inclusion of SiO2 enlarges the optical band gap and suppresses the grain growth up to 4 nm in size. High TiO2 dispersion in SiO2 matrix was observed for all mixed materials. The refractive index (at λ = 600 nm) increases linearly with composition from 1.48 (in 100% SiO2) to 2.22 (in 100% TiO2) leading to lower dense material, its dispersion being discussed in terms of the Wemple-DiDomenico single oscillator model. Hence, the optical parameters, such optical dispersion energies E0 and Ed, the average oscillators, strength S0 and wavelength λ0 and the ratio of the carrier concentration to the effective mass N/m∗ have been derived. The analysis revealed a strong dependence on composition and structure. The optical response was also investigated in term of complex optical conductivity (σ) and both volume and surface energy loss functions (VELF and SELF).

  18. Ag-TiO2 nanoparticle codoped SiO2 films on ZrO2 barrier-coated glass substrates with antibacterial activity in ambient condition.

    PubMed

    Mukhopadhyay, Anindita; Basak, Sujit; Das, Jugal Kishore; Medda, Samar Kumar; Chattopadhyay, Krishnananda; De, Goutam

    2010-09-01

    Anatase TiO2 and Ag nanoparticles (NPs) codoped SiO2 films were prepared by the sol-gel method. Proportionate amounts of 3-(glycidoxypropyl)trimethoxysilane (GLYMO), tetraethylorthosilicate (TEOS) and 3-(methacryloxypropyl)trimethoxysilane (MEMO) derived inorganic-organic silica sol, commercially available dispersed anatase TiO2 NPs, and AgNO3 were used to prepare the sols. The films were prepared on ZrO2 (cubic) precoated soda-lime glass substrates by a single-dipping technique and heat-treated at 450 °C in air and H2/Ar atmosphere to obtain hard, relatively porous, and transparent coatings of thickness>600 nm. The ZrO2 barrier layer was previously applied on soda-lime glass to restrict the diffusion of Ag into the substrate. The Ag-TiO2 NPs incorporated SiO2 films were intense yellow in color and found to be fairly stable at ambient condition for several days under fluorescent light. These films show a considerable growth inhibition on contact with the gram negative bacteria E. coli.

  19. Aggregation of dipolar molecules in SiO2 hybrid organic-inorganic films: use of silver nanoparticles as inhibitors of molecular aggregation

    NASA Astrophysics Data System (ADS)

    Franco, Alfredo; García-Macedo, Jorge; Brusatin, Giovanna; Guglielmi, Massimo

    2013-04-01

    The technological implementation of hybrid organic-inorganic materials in second order nonlinear optical photonic devices depends strongly on the ability of the host matrixes to contain high loads of dipolar molecules without aggregation. Some organic molecules are often used to diminish the attracting interactions between dipolar molecules in such kind of materials, but their efficiency as inhibitors of molecular aggregation is limited by their polarizability. In this work, we report the use of silver nanoparticles as inhibitors of molecular aggregation in hybrid organic-inorganic films doped with dipolar molecules. The large polarizability of the silver nanoparticles makes them ideal moieties for the inhibition of the electrostatic interactions between dipolar nonlinear optical molecules. The average size of the silver nanoparticles in this work was 70.5 nm in diameter, they were synthesized using silver nitrate (AgNO3) as precursor and aminoethylaminopropyltrimethoxysilane as reducing agent. These nanoparticles were immersed in SiO2 hybrid organic-inorganic sol-gel films doped with dipolar chromophores to study their effect as inhibitors of dipolar chromophores aggregation. The presence of the silver nanoparticles in the solid films was confirmed by transmission electronic microscopy and UV-Visible spectroscopy. UV-Visible spectroscopy was also used to monitor the dipolar chromophores aggregation in the SiO2 films. We found that, at room temperature, silver nanoparticles are good inhibiting chromophores aggregation in comparison with the performance of organic inhibitors.

  20. Effect of SiO2 addition on photocatalytic activity, water contact angle and mechanical stability of visible light activated TiO2 thin films applied on stainless steel by a sol gel method

    NASA Astrophysics Data System (ADS)

    Momeni, Mansour; Saghafian, Hasan; Golestani-Fard, Farhad; Barati, Nastaran; Khanahmadi, Amirhossein

    2017-01-01

    Nanostructured N doped TiO2/20%SiO2 thin films were developed on steel surface via sol gel method using a painting airbrush. Thin films then were calcined at various temperatures in a range of 400-600 °C. The effect of SiO2 addition on phase composition and microstructural evolution of N doped TiO2 films were studied using XRD and FESEM. Optical properties, visible light photocatalytic activity, hydrophilic behavior, and mechanical behavior of the films were also investigated by DRS, methylene blue degradation, water contact angle measurements, and nanoscratch testing. Results indicated that the band gap energy of N doped TiO2/SiO2 was increased from 2.93 to 3.09 eV. Crack formation during calcination was also significantly promoted in the composite films. All composite films demonstrated weaker visible light photocatalytic activities and lower mechanical stability in comparison with N doped TiO2 films. Moreover, the N doped TiO2/SiO2 film calcined at 600 °C showed undesirable hydrophilic behavior with a water contact angle of 57° after 31 h of visible light irradiation. Outcomes of the present study reveal some different results to previous reports on TiO2/SiO2 films. In general, we believe the differences in substrate material as well as application in visible light are the main reasons for the above mentioned contradiction.

  1. Spin-wave modes in granular superferromagnetic (SiO2)Co/GaAs films observed using Brillouin light scattering

    NASA Astrophysics Data System (ADS)

    Stashkevich, A. A.; Roussigné, Y.; Stognij, A. I.; Novitskii, N. N.; Kostylev, M. P.; Wurtz, G. A.; Zayats, A. V.; Lutsev, L.

    2008-12-01

    Behavior of dipole-exchange spin waves (SWs) in the Damon-Eshbach geometry in a nanocomposite (SiO2)100-xCox superferromagnetic (x=80at.%) film has been studied by Brillouin light scattering. The measured value of the effective exchange constant turned out to be three times less than its value for the bulk cobalt. A qualitative theoretical model has been proposed to explain this reduction. It has been shown that the “superspin” approximation, identifying each nanoparticle with a “magnetic point” with no internal structure, is not sufficient to account for the description of the SW behavior of a concentrated nanocomposite medium.

  2. Brillouin light scattering observation of the transition from the superparamagnetic to the superferromagnetic state in nanogranular (SiO2)Co films

    NASA Astrophysics Data System (ADS)

    Stashkevich, A. A.; Roussigné, Y.; Djemia, P.; Billet, D.; Stognij, A. I.; Novitskii, N. N.; Wurtz, G. A.; Zayats, A. V.; Viau, G.; Chaboussant, G.; Ott, F.; Gautrot, S.; Kostylev, M. P.; Lutsev, L. V.; Belotelov, V.

    2008-11-01

    Evolution of magnetic excitations from purely magnetostatic modes to dipole-exchange spin waves in the Damon-Eshbach geometry in nanocomposite (SiO2)100-xCox (50 at. %films during a transition from superparamagnetic to superferromagnetic state has been studied by Brillouin light scattering. It has been shown that removal of the degeneracy of backward volume magnetostatic waves due to nonzero exchange constant manifests itself in more pronounced Stokes/anti-Stokes asymmetry. Accompanying static characterization by means of magnetic force microscopy imaging and grazing incidence small angle neutron scattering has demonstrated the presence of weak stripe domains in the superferromagnetic phase.

  3. Rhodamine 6G and 800 J-heteroaggregates with enhanced acceptor luminescence (HEAL) adsorbed in transparent SiO2 GLAD thin films.

    PubMed

    Sánchez-Valencia, Juan R; Aparicio, Francisco J; Espinós, Juan P; Gonzalez-Elipe, Agustín R; Barranco, Angel

    2011-04-21

    An enhanced fluorescent emission in the near infrared is observed when the Rhodamine 800 (Rh800) and 6G (Rh6G) dyes are coadsorbed in porous SiO(2) optical thin films prepared by glancing angle deposition (GLAD). This unusual behavior is not observed in solution and it has been ascribed to the formation of a new type of J-heteroaggregates with enhanced acceptor luminescence (HEAL). This article describes in detail and explains the main features of this new phenomenology previously referred in a short communication [J. R. Sánchez-Valencia, J. Toudert, L. González-García, A. R. González-Elipe and A. Barranco, Chem. Commun., 2010, 46, 4372-4374]. It is found that the efficiency and characteristics of the energy transfer process are dependent on the Rh6G/Rh800 concentration ratio which can be easily controlled by varying the pH of the solutions used for the infiltration of the molecules or by thermal treatments. A simple model has been proposed to account for the observed enhanced acceptor luminescence in which the heteroaggregates order themselves according to a "head to tail" configuration due to the geometrical constrains imposed by the SiO(2) porous matrix thin film. The thermal stability of the dye molecules within the films and basic optical (absorption and fluorescence) principles of the HEAL process are also described.

  4. Detection of short range order in SiO2 thin-films by grazing-incidence wide and small-angle X-ray scattering

    NASA Astrophysics Data System (ADS)

    Nagata, Kohki; Ogura, Atsushi; Hirosawa, Ichiro; Suwa, Tomoyuki; Teramoto, Akinobu; Ohmi, Tadahiro

    2016-04-01

    The effects of the fabrication process conditions on the microstructure of silicon dioxide thin films of <10 nm thickness are presented. The microstructure was investigated using grazing-incidence wide and small-angle X-ray scattering methods with synchrotron radiation. The combination of a high brilliance light source and grazing incident configuration enabled the observation of very weak diffuse X-ray scattering from SiO2 thin films. The results revealed different microstructures, which were dependent on oxidizing species or temperature. The micro-level properties differed from bulk properties reported in the previous literature. It was indicated that these differences originate from inner stress. The detailed structure in an amorphous thin film was not revealed owing to detection difficulties.

  5. Room-temperature NH3 gas sensors based on Ag-doped γ-Fe2O3/SiO2 composite films with sub-ppm detection ability.

    PubMed

    Tang, Yongliang; Li, Zhijie; Zu, Xiaotao; Ma, Jinyi; Wang, Lu; Yang, Jing; Du, Bo; Yu, Qingkai

    2015-11-15

    In this report, NH3 gas sensors based on Ag-doped γ-Fe2O3/SiO2 composite films are investigated. The composite films were prepared with a sol-gel process, and the films' electrical resistance responded to the change of NH3 concentration in the environment. The SEM and AFM investigations showed that the films had a porous structure, and the XRD investigation indicated that the size of Ag particles changed with the modification of Ag loading content. Through a comparative gas sensing study among the Ag-doped composite films, undoped composite film, γ-Fe2O3 film, and SiO2 film, the Ag-doped composite films were found to be much more sensitive than the sensors based on the undoped composite film and γ-Fe2O3 film at room temperature, indicating the significant influences of the SiO2 and Ag on the sensing property. Moreover, the sensor based on Ag-doped (4%) γ-Fe2O3/SiO2 composite film was able to detect the NH3 gas at ppb level. Conversely, the responses of the sensor to other test gases (C2H5OH, CO, H2, CH4 and H2S) were all markedly low, suggesting excellent selectivity.

  6. High-conductivity SiO2-matrix B-doped Si-NC thin films by following ion-beam treatment

    NASA Astrophysics Data System (ADS)

    Huang, Junjun; Wang, Weiyan; Yang, Jie; Tan, Yongzhen; Chen, Wei; Ge, Tianyu; Zhang, Yajun; Gao, Min; Chen, Zhenming

    2016-09-01

    In this work, further ion-beam was performed on SiO2-matrix B-doped Si-NC (SBC) thin films in order to enhance conductivity. The effect of ionbeam type on the electrical properties of SBC thin films was investigated systematically. The results indicated that the conductivities of SBC thin films were significantly improved by both argon and hydrogen ion-beam treatments, and the higher the hydrogen ion ratio, the higher the conductivity of SBC thin films. The conductivity of SBC thin films was increased from 1.82 × 10-6 S/cm to 3.2 × 10-3 S/cm with following hydrogen-ion-beam treatment. The change in conductivity of SBC thin films was most possibly resultant from the ion-beam treatment facilitating the formation of higher superficial order and lower defects. An alternative method was proposed to prepare high-conductivity SBC thin films, which may be applied to other heterogeneous thin films.

  7. Water adsorption, solvation and deliquescence of alkali halide thin films on SiO2 studied by ambient pressure X-ray photoelectron spectroscopy

    SciTech Connect

    Arima, Kenta; Jiang, Peng; Deng, Xingyi; Bluhm, Henrik; Salmeron, Miquel

    2010-03-31

    The adsorption of water on KBr thin films evaporated onto SiO2 was investigated as a function of relative humidity (RH) by ambient pressure X-ray photoelectron spectroscopy. At 30percent RH adsorbed water reaches a coverage of approximately one monolayer. As the humidity continues to increase, the coverage of water remains constant or increases very slowly until 60percent RH, followed by a rapid increase up to 100percent RH. At low RH a significant number of the Br atoms are lost due to irradiation damage. With increasing humidity solvation increases ion mobility and gives rise to a partial recovery of the Br/K ratio. Above 60percent RH the increase of the Br/K ratio accelerates. Above the deliquescence point (85percent RH), the thickness of the water layer continues to increase and reaches more than three layers near saturation. The enhancement of the Br/K ratio at this stage is roughly a factor 2.3 on a 0.5 nm KBr film, indicating a strong preferential segregation of Br ions to the surface of the thin saline solution on SiO2.

  8. Optimization of a Solution-Processed SiO2 Gate Insulator by Plasma Treatment for Zinc Oxide Thin Film Transistors.

    PubMed

    Jeong, Yesul; Pearson, Christopher; Kim, Hyun-Gwan; Park, Man-Young; Kim, Hongdoo; Do, Lee-Mi; Petty, Michael C

    2016-01-27

    We report on the optimization of the plasma treatment conditions for a solution-processed silicon dioxide gate insulator for application in zinc oxide thin film transistors (TFTs). The SiO2 layer was formed by spin coating a perhydropolysilazane (PHPS) precursor. This thin film was subsequently thermally annealed, followed by exposure to an oxygen plasma, to form an insulating (leakage current density of ∼10(-7) A/cm(2)) SiO2 layer. Optimized ZnO TFTs (40 W plasma treatment of the gate insulator for 10 s) possessed a carrier mobility of 3.2 cm(2)/(V s), an on/off ratio of ∼10(7), a threshold voltage of -1.3 V, and a subthreshold swing of 0.2 V/decade. In addition, long-term exposure (150 min) of the pre-annealed PHPS to the oxygen plasma enabled the maximum processing temperature to be reduced from 180 to 150 °C. The resulting ZnO TFT exhibited a carrier mobility of 1.3 cm(2)/(V s) and on/off ratio of ∼10(7).

  9. Light induced water oxidation on cobalt-phosphate (Co-Pi) catalyst modified semi-transparent, porous SiO2-BiVO4 electrodes.

    PubMed

    Pilli, Satyananda Kishore; Deutsch, Todd G; Furtak, Thomas E; Turner, John A; Brown, Logan D; Herring, Andrew M

    2012-05-21

    A facile and simple procedure for the synthesis of semi-transparent and porous SiO2-BiVO4 electrodes is reported. The method involves a surfactant assisted metal-organic decomposition at 500 °C. An earth abundant oxygen evolution catalyst (OEC), cobalt phosphate (Co-Pi), has been used to modify the SiO2-BiVO4 electrode by electrodeposition (ED) and photoassisted electrodeposition (PED) methods. Modified electrodes by these two methods have been examined for light induced water oxidation and compared to the unmodified SiO2-BiVO4 electrodes by various photoelectrochemical techniques. The PED method was a more effective method of OEC preparation than the ED method as evidenced by an increased photocurrent magnitude during photocurrent-potential (I-V) characterizations. Electrode surfaces catalyzed by PED exhibited a very large cathodic shift (∼420 mV) in the onset potential for water oxidation. The chopped-light I-V measurements performed at different intervals over 24-hour extended testing under illumination and applied bias conditions show a fair photostability for PED Co-Pi modified SiO2-BiVO4.

  10. Growth of residual stress-free ZnO films on SiO2/Si substrate at room temperature for MEMS devices

    NASA Astrophysics Data System (ADS)

    Singh, Jitendra; Ranwa, Sapana; Akhtar, Jamil; Kumar, Mahesh

    2015-06-01

    ZnO thick Stress relaxed films were deposited by reactive magnetron sputtering on 2"-wafer of SiO2/Si at room temperature. The residual stress of ZnO films was measured by measuring the curvature of wafer using laser scanning method and found in the range of 0.18 x 109 to 11.28 x 109 dyne/cm2 with compressive in nature. Sputter pressure changes the deposition rates, which strongly affects the residual stress and surface morphologies of ZnO films. The crystalline wurtzite structure of ZnO films were confirmed by X-ray diffraction and a shift in (0002) diffraction peak of ZnO towards lower 2θ angle was observed with increasing the compressive stress in the films. The band gap of ZnO films shows a red shift from ˜3.275 eV to ˜3.23 eV as compressive stress is increased, unlike the stress for III-nitride materials. A relationship between stress and band gap of ZnO was derived and proposed. The stress-free growth of piezoelectric films is very important for functional devices applications.

  11. X-ray diffraction and surface acoustic wave analysis of BST/Pt/TiO2/SiO2/Si thin films

    NASA Astrophysics Data System (ADS)

    Mseddi, Souhir; Njeh, Anouar; Schneider, Dieter; Fuess, Hartmut; Hédi Ben Ghozlen, Mohamed

    2011-11-01

    High dielectric constant and electrostriction property of (Ba, Sr)Ti03 (BST) thin films result in an increasing interest for dielectric devices and microwave acoustic resonator. Barium strontium titanate (Ba0.645Sr0.355TiO3) films of about 300 nm thickness are grown on Pt(111)/TiO2/SiO2/Si(001) substrates by rf magnetron sputtering deposition techniques. X-ray diffraction is applied for the microstructural characterization. The BST films exhibit a cubic perovskite structure with a dense and smooth surface. A laser acoustic waves (LA-waves) technique is used to generate surface acoustic waves (SAW) propagating in the BST films. Young's modulus E and the Poisson ratio ν of TiO2, Pt and BST films in different propagation directions are derived from the measured dispersion curves. Estimation of BST elastics constants are served in SAW studies. Impact of stratification process on SAW, propagating along [100] and [110] directions of silicon substrate, has been interpreted on the basis of ordinary differential equation (ODE) and stiffness matrix method (SMM). A good agreement is observed between experimental and calculated dispersion curves. The performed calculations are strongly related to the implemented crystallographic data of each layer. Dispersion curves are found to be sensitive to the SAW propagation direction and the stratification process for the explored frequency ranges 50-250 MHz, even though it corresponds to a wave length clearly higher than the whole films thickness.

  12. Detection of λ-cyhalothrin by a core-shell spherical SiO2-based surface thin fluorescent molecularly imprinted polymer film.

    PubMed

    Gao, Lin; Han, Wenjuan; Li, Xiuying; Wang, Jixiang; Yan, Yongsheng; Li, Chunxiang; Dai, Jiangdong

    2015-12-01

    A fluorescent core-shell molecularly imprinted polymer based on the surface of SiO2 beads was synthesized and its application in the fluorescence detection of ultra-trace λ-cyhalothrin (LC) was investigated. The shell was prepared by copolymerization of acrylamide with allyl fluorescein in the presence of LC to form recognition sites. The experimental results showed that the thin fluorescent molecularly imprinted polymer (FMIP) film exhibited better selective recognition ability than fluorescent molecularly non-imprinted polymer (FNIP). A new nonlinear relationship between quenching rate and concentration was found in this work. In addition, the nonlinear relationship allowed a lower concentration range of 0-5.0 nM to be described by the Stern-Volmer equation with a correlation coefficient of 0.9929. The experiment results revealed that the SiO2@FMIP was satisfactory as a recognition element for determination of LC in soda water samples. Therefore this study demonstrated the potential of MIP for the recognition and detection of LC in food.

  13. SiO2 substrate and Mo,In codoping effect on crystalline and vibrational characteristics of ZnO sprayed thin films

    NASA Astrophysics Data System (ADS)

    Souissi, A.; Mimouni, R.; Amlouk, M.; Guermazi, S.

    2015-09-01

    Undoped ZnO and codoped ZnO:Mo:In thin films were deposited on an amorphous SiO2 substrate at 460 °C using a (Mo/Zn) molar ratio of 1% and (In/Zn) ratios of 1%, 2%, 3% and 10%. The thin films were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Raman spectroscopy (RS). The results revealed that the average crystallite sizes ranged from 36.2 to 18.97 nm, decreasing uniformly with the increase of co-doping. They were also lower than the grain size values of 48.29, 51.38, 60.59, 36.76, and 54.52 nm and dependent on the evolution of the residual compressive stress values, namely 0.358, 0.314, 0.569, 0.278 and 0.108 GPa, without and with the co-doping, respectively. The non-uniformities recorded at In 2% could presumably be attributed to the variable effect of the SiO2 substrate and dopants on the formation of ZnO:Mo:In thin films. Raman spectroscopy confirmed the findings from structural analysis, showing that all samples crystallized following the hexagonal Wurtzite single phase. It highlighted the presence of two dominant bands, 1LO and 2LO, whose ∼71 and 137 meV energies were comparable and above the ZnO exciton binding energy of 60 meV. The 2LO band showed marked dependencies on the physicochemical parameters mentioned above. The strong bands noted for optimal co-doping at Mo 1% and In 3% can be used (tested) in various electrical and optoelectronic applications.

  14. Substituent effects on packing entropy and film morphologies in the nucleation of functionalized pentacenes on SiO2 substrate: molecular dynamics simulations.

    PubMed

    Chen, Shuang; Ma, Jing

    2012-08-21

    The changes in structural ordering, packing entropy, free energy, and film morphologies in the initial nucleation processes of pentacene (Pn), 6, 13-bis(t-butylethynyl) pentacene (t-Bu Pn), and 6, 13-bis(triisopropylsilylethynyl) pentacene (TIPS Pn) on the SiO(2) substrate were investigated, by using the molecular dynamics simulations. During the nucleation, the rod-like Pn molecules tend to diffuse rapidly and have different orientations on the SiO(2) surface. At the low coverage, the t-Bu Pn and TIPS Pn molecules with the branched topological structures almost lie flat on the substrate. On the basis of statistical distribution of various packing configurations of the functionalized Pn pairs, the packing entropy is estimated according to the Boltzmann formula. The packing entropy abruptly decreases in the early stage of deposition. Once the critical nucleus size is reached, the packing entropy converges to a constant value. As the coverage increases, the monolayer films of Pn and its branched derivatives become more ordered. The TIPS Pn with the relatively larger molecular area would occasionally stand on the surface during the nucleation, resulting in the dramatic changes in free energy. In the monolayers, the functionalized Pn molecules are packing more orderly than those in amorphous solids, but less orderly than those in crystals. The degree of order of these monolayers increases as the size of the substituents increases. The understanding of substituent effects on nucleation processes and packing structures is helpful to fabricate organic thin films with well-predefined molecular orientations.

  15. Solution-Processed VO2-SiO2 Composite Films with Simultaneously Enhanced Luminous Transmittance, Solar Modulation Ability and Anti-Oxidation property

    NASA Astrophysics Data System (ADS)

    Zhao, Lili; Miao, Lei; Liu, Chengyan; Li, Chao; Asaka, Toru; Kang, Yipu; Iwamoto, Yuji; Tanemura, Sakae; Gu, Hui; Su, Huirong

    2014-11-01

    Recently, researchers spare no efforts to fabricate desirable vanadium dioxide (VO2) film which provides simultaneously high luminous transmittance and outstanding solar modulation ability, yet progress towards the optimization of one aspect always comes at the expense of the other. Our research devotes to finding a reproducible economic solution-processed strategy for fabricating VO2-SiO2 composite films, with the aim of boosting the performance of both aspects. Compare to VO2 film, an improvement of 18.9% (from 29.6% to 48.5%) in the luminous transmittance as well as an increase of 6.0% (from 9.7% to 15.7%) in solar modulation efficiency is achieved when the molar ratio of Si/V attains 0.8. Based on the effective medium theory, we simulate the optical spectra of the composite films and the best thermochromic property is obtained when the filling factor attains 0.5, which is consistent with the experimental results. Meanwhile, the improvement of chemical stability for the composite film against oxidation has been confirmed. Tungsten is introduced to reduce the phase transition temperature to the ambient temperature, while maintain the thermochromism required for application as smart window. Our research set forth a new avenue in promoting practical applications of VO2-based thermochromic fenestration.

  16. Solution-Processed VO2-SiO2 Composite Films with Simultaneously Enhanced Luminous Transmittance, Solar Modulation Ability and Anti-Oxidation property

    PubMed Central

    Zhao, Lili; Miao, Lei; Liu, Chengyan; Li, Chao; Asaka, Toru; Kang, Yipu; Iwamoto, Yuji; Tanemura, Sakae; Gu, Hui; Su, Huirong

    2014-01-01

    Recently, researchers spare no efforts to fabricate desirable vanadium dioxide (VO2) film which provides simultaneously high luminous transmittance and outstanding solar modulation ability, yet progress towards the optimization of one aspect always comes at the expense of the other. Our research devotes to finding a reproducible economic solution-processed strategy for fabricating VO2-SiO2 composite films, with the aim of boosting the performance of both aspects. Compare to VO2 film, an improvement of 18.9% (from 29.6% to 48.5%) in the luminous transmittance as well as an increase of 6.0% (from 9.7% to 15.7%) in solar modulation efficiency is achieved when the molar ratio of Si/V attains 0.8. Based on the effective medium theory, we simulate the optical spectra of the composite films and the best thermochromic property is obtained when the filling factor attains 0.5, which is consistent with the experimental results. Meanwhile, the improvement of chemical stability for the composite film against oxidation has been confirmed. Tungsten is introduced to reduce the phase transition temperature to the ambient temperature, while maintain the thermochromism required for application as smart window. Our research set forth a new avenue in promoting practical applications of VO2-based thermochromic fenestration. PMID:25384345

  17. Thin film transistors with wurtzite ZnO channels grown on Si3N4/SiO2/Si (111) substrates by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Rogers, D. J.; Sandana, V. E.; Teherani, F. Hosseini; Razeghi, M.

    2010-03-01

    Thin Film Transistors (TFT) were made by growing ZnO on Si3N4/SiO2/Si (111) substrates by pulsed laser deposition. X-ray diffraction and scanning electron microscope studies revealed the ZnO to have a polycrystalline wurtzite structure with a smooth surface, good crystallographic quality and a strong preferential c-axis orientation. Transmission studies in similar ZnO layers on glass substrates showed high transmission over the whole visible spectrum. Electrical measurements of a back gate geometry FET showed an enhancement-mode response with hard saturation, mA range Id and a VON ~ 0V. When scaled down, such TFTs may be of interest for high frequency applications.

  18. Study of the picosecond laser damage in HfO2/SiO2-based thin-film coatings in vacuum

    NASA Astrophysics Data System (ADS)

    Kozlov, A. A.; Papernov, S.; Oliver, J. B.; Rigatti, A.; Taylor, B.; Charles, B.; Smith, C.

    2016-12-01

    The laser damage thresholds of various HfO2/SiO2-based thin film coatings, including multilayer dielectric (MLD) gratings and high reflectors of different designs, prepared by E-beam and Plasma Ion Assisted Deposition (PIAD) methods, were investigated in vacuum, dry nitrogen, and after air-vacuum cycling. Single and multiple-pulse damage thresholds and their pulse-length scaling in the range of 0.6 to 100 ps were measured using a vacuum damage test station operated at 1053nm. The E-beam deposited high reflectors showed higher damage thresholds with square-root pulse-length scaling, as compared to PIAD coatings, which typically show slower power scaling. The former coatings appeared to be not affected by air/vacuum cycling, contrary to PIAD mirrors and MLD gratings. The relation between 1-on-1 and N-on-1 damage thresholds was found dependent on coating design and deposition methods.

  19. Effects of defects generated in ALD TiO2 films on electrical properties and interfacial reaction in TiO2/SiO2/Si system upon annealing in vacuum

    NASA Astrophysics Data System (ADS)

    Won, Sanghee; Go, Seunghee; Lee, Wonhee; Jeong, Kyunghoon; Jung, Hyunsuk; Lee, Chongmu; Lee, Eungu; Lee, Jaegab

    2008-12-01

    Thin TiO2 layers grown at 130°C on SiO2-coated Si substrates by atomic layer deposition (ALD) using TTIP and H2O as precursors were annealed, and the effects of the annealing temperature on the resulting electrical properties of TiO2 and the interface properties between a Pt electrode and TiO2 were examined using transmission line model (TLM) structures. The as-deposited TiO2 thin film had an amorphous structure with OH groups and a high resistivity of 6×103Ω-cm. Vacuum annealing at 700 °C transformed the amorphous film into an anatase structure and reduced its resistivity to 0.04Ω-cm. In addition, the vacuum-annealing of the TiO2/SiO2 structure at 700°C produced free silicon at the TiO2-SiO2 interface as a result of the reaction between the Ti interstitials and SiO2. The SiO2 formed on the TiO2 surface caused a Schottky contact, which was characterized by the TLM method. The use of the TLM method enabled the accurate measurement of the resistivity of the vacuum-annealed TiO2 films and the characterization of the Schottky contacts of the metal electrode to the TiO2.

  20. Thickness of the {SiO2}/{Si} interface and composition of silicon oxide thin films: effect of wafer cleaning procedures

    NASA Astrophysics Data System (ADS)

    Stedile, F. C.; Baumvol, I. J. R.; Oppenheim, I. F.; Trimaille, I.; Ganem, J.-J.; Rigo, S.

    1996-09-01

    We determined the areal density of Si atoms constituting the oxide-silicon interface and the stoichiometry of ultra-thin silicon oxide films, thermally grown on Si(001) in dry 18O 2 atmospheres, using the channeling of α-particles along the <001> axis of the Si substrates associated with grazing angle detection of the scattered particles. The amount of 18O atoms in the films was determined independently using the 18O(p,α) 15N nuclear reaction at 730 keV. The Si wafers were submitted to different cleaning procedures before oxidation in 18O 2, namely: standard RCA cleaning, HF etching followed by a rinse in ethanol and rapid thermal cleaning (RTC) under high vacuum. The stoichiometry of all oxide films having thicknesses between 2 and 13 nm could be fitted assuming a ratio {O}/{Si} = 2 , that is, the films were constituted by silicon dioxide. By comparing the results for samples cleaned in different ways, however, we noticed a pronounced change in the number of atoms in the non-registered Si layers at the {SiO2}/{Si} interface and so in the thickness of these interfaces.

  1. High frequency capacitance-voltage characteristics of thermally grown SiO2 films on beta-SiC

    NASA Technical Reports Server (NTRS)

    Tang, S. M.; Berry, W. B.; Kwor, R.; Zeller, M. V.; Matus, L. G.

    1990-01-01

    Silicon dioxide films grown under dry and wet oxidation environment on beta-SiC films have been studied. The beta-SiC films had been heteroepitaxially grown on both on-axis and 2-deg off-axis (001) Si substrates. Capacitance-voltage and conductance-voltage characteristics of metal-oxide-semiconductor structures were measured in a frequency range of 10 kHz to 1 MHz. From these measurements, the interface trap density and the effective fixed oxide charge density were observed to be generally lower for off-axis samples.

  2. [Stimulated emission characteristics of ZnO thin films deposited by magnetron sputtering on SiO2 substrates].

    PubMed

    Jing, Wang; Xi-qing, Zhang; Xiao-ying, Teng; De-ping, Xiong; Peng, Lin; Li, Wang; Shi-hua, Huang

    2004-07-01

    ZnO thin films were deposited by magnetron sputtering on SiQ2 substrates. The temperature dependence of the absorption spectra and the photoluminescence spectra was studied for ZnO thin film. The absorption of the longitudinal optical (LO) phonons and the free-excitons was observed at room temperature. The free-exciton emission was only observed in PL spectra at room temperature, the results indicate that ZnO thin films have excellent quality and low density of defects. The stimulated emission properties of ZnO thin films were investigated. When excitation intensity is above threshold, the FWHM o f stimulated emission peak increases and stimulated emission peak shows red shift with increasing excitation intensity. Our analysis shows that the optical gain is due to electronhole plasma emission.

  3. Atomic layer deposition of SiO2 thin films using tetrakis(ethylamino)silane and ozone.

    PubMed

    Kim, Jae-Kyung; Jin, Kwangsun; Jung, Jongwan; Rha, Sa-Kyun; Lee, Won-Jun

    2012-04-01

    We examined the atomic layer deposition (ALD) of silicon dioxide thin films on a silicon wafer by alternating exposures to tetrakis(ethylamino)silane [Si(NHC2H5)4] and O3. The growth kinetics of silicon oxide films was examined at substrate temperatures ranging from 325 to 514 degrees C. The deposition was governed by a self-limiting surface reaction, and the growth rate at 478 degrees C was saturated at 0.17 nm/cycle for Si(NHC2H5)4 exposures of 2 x 10(6) L (1 L = 10(-6) Torr x s). The films deposited at 365-404 degrees C exhibited a higher deposition rate of 0.20-0.21 nm/cycle. However, they contained impurities, such as carbon and nitrogen, and showed poor film qualities. The concentration of impurities decreased with increasing substrate temperature. It was found that the films deposited in the high-temperature regime (478-514 degrees C) showed excellent physical and electrical properties equivalent to those of LPCVD films.

  4. Fabrication of mechanically robust, self-cleaning and optically high-performance hybrid thin films by SiO2&TiO2 double-shelled hollow nanospheres

    NASA Astrophysics Data System (ADS)

    Yao, Lin; He, Junhui; Geng, Zhi; Ren, Tingting

    2015-07-01

    Low-cost antireflection (AR) thin films on large-area optical surfaces are important for high-performance optical devices, display devices and photovoltaic cells. In the current work, SiO2&TiO2 double-shell hollow nanospheres (DSHNs) were designed, synthesized and utilized as building blocks for fabricating multifunctional AR thin films. By optimizing the porosity of SiO2&TiO2 DSHN and thin film structure, substrates with DSHN thin films attained transmittance as high as 99.4% and average transmittance up to 98.5% in the visible region. The nano-composite SiO2-TiO2 films exhibited intrinsic superhydrophilicity, anti-fogging and high photocatalytic activity. Tape peeling test, sponge washing test, and high temperature and moisture proof test showed favorable robustness and functional durability of the thin films, which make them extremely attractive for applications in lenses, photovoltaic cells and windows of high-rise buildings.Low-cost antireflection (AR) thin films on large-area optical surfaces are important for high-performance optical devices, display devices and photovoltaic cells. In the current work, SiO2&TiO2 double-shell hollow nanospheres (DSHNs) were designed, synthesized and utilized as building blocks for fabricating multifunctional AR thin films. By optimizing the porosity of SiO2&TiO2 DSHN and thin film structure, substrates with DSHN thin films attained transmittance as high as 99.4% and average transmittance up to 98.5% in the visible region. The nano-composite SiO2-TiO2 films exhibited intrinsic superhydrophilicity, anti-fogging and high photocatalytic activity. Tape peeling test, sponge washing test, and high temperature and moisture proof test showed favorable robustness and functional durability of the thin films, which make them extremely attractive for applications in lenses, photovoltaic cells and windows of high-rise buildings. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr02467f

  5. Optical properties of ion-beam-synthesized Au nanoparticles in SiO2 matrix

    NASA Astrophysics Data System (ADS)

    Hsieh, Chang-Lin; Oyoshi, Keiji; Chao, Der-Sheng; Tsai, Hsu-Sheng; Hong, Wei-Lun; Takeda, Yoshihiko; Liang, Jenq-Horng

    2016-05-01

    In recent years, gold (Au) nanoparticles have been synthesized via various methods and used in optical and biomedical detection. Au nanoparticles contain some remarkable dimension-dependent optical properties due to surface plasmon resonance (SPR) in Au nanoparticles which causes high absorption in visible light regions. Since SPR in well-crystallized Au nanoparticles can enhance the local electromagnetic field, it is thus expected that greater efficiency in the photoluminescence (PL) originating from oxygen deficiency centers (ODC) can be achieved in Au-implanted SiO2 matrix. In order to demonstrate the enhancement of PL, Au nanoparticles were formed in SiO2 film using ion beam synthesis and their optical and microstructural properties were also investigated in this study. The results revealed that a clear absorption peak at approximately 530 nm was identified in the UV-Vis spectra and was attributed to SPR induced by Au nanoparticles in SiO2. The SPR of Au nanoparticles is also dependent on thermal treatment conditions, such as post-annealing temperature and ambient. The Au nanoparticle-containing SiO2 film also displayed several distinctive peaks at approximately 320, 360, 460, and 600 nm in the PL spectra and were found to be associated with ODC-related defects and non-bridging oxygen hole centers (NBOHC) in SiO2. In addition, the PL peak intensities increased as post-annealing temperature increased, a finding contradictory to the defect recovery but highly consistent with the SPR tendency. A maximum PL emission was achieved when the Au-implanted SiO2 film was annealed at 1100 °C for 1 h under N2. Therefore, the existence of Au nanoparticles in SiO2 film can induce SPR effects as well as enhance PL emission resulting from defect-related luminescence centers.

  6. Fabrication and characterization of Er+3 doped SiO2/SnO2 glass-ceramic thin films for planar waveguide applications

    NASA Astrophysics Data System (ADS)

    Guddala, S.; Chiappini, A.; Armellini, C.; Turell, S.; Righini, G. C.; Ferrari, M.; Narayana Rao, D.

    2015-02-01

    Glass-ceramics are a kind of two-phase materials constituted by nanocrystals embedded in a glass matrix and the respective volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramics. Among these properties transparency is crucial in particular when confined structures, such as, dielectric optical waveguides, are considered. Moreover, the segregation of dopant rare-earth ions, like erbium, in low phonon energy crystalline medium makes these structures more promising in the development of waveguide amplifiers. Here we are proposing a new class of low phonon energy tin oxide semiconductor medium doped silicate based planar waveguides. Er3+ doped (100-x) SiO2-xSnO2 (x= 10, 20, 25 and 30mol%), glass-ceramic planar waveguide thin films were fabricated by a simple sol-gel processing and dip coating technique. XRD and HRTEM studies indicates the glass-ceramic phase of the film and the dispersion of ~4nm diameter of tin oxide nanocrystals in the amorphous phase of silica. The spectroscopic assessment indicates the distribution of the dopant erbium ions in the crystalline medium of tin oxide. The observed low losses, 0.5±0.2 dB/cm, at 1.54 μm communication wavelength makes them a quite promising material for the development of high gain integrated optical amplifiers.

  7. Optical and physical properties of solgel-derived GeO2:SiO2 films in photonic applications.

    PubMed

    Ho, Charles K F; Pal, Rajni; Djie, H S; Pita, Kantisara; Ngo, Nam Quoc; Osipowicz, T

    2007-07-10

    The functionality of optical components relies heavily on the composition-dependent properties of germanosilicate materials, which include the refractive index, photosensitivity, and microstructural properties. Recent studies and parallel developments are presented of germanosilicate films with composition x of Ge content (i.e., xGeO(2):(1-x)SiO(2)) that were synthesized by the solgel process for various integrated photonic applications undertaken. The following novel aspects are discussed with respect to the effect of composition of the glassy films (0.05

  8. Continuous ultrathin silver films deposited on SiO2 and SiNx using a self-assembled monolayer

    NASA Astrophysics Data System (ADS)

    Hafezian, Soroush; Maloney, Kate; Lefebvre, Josianne; Martinu, Ludvik; Kéna-Cohen, Stéphane

    2016-09-01

    In this letter, we study the deposition of ultrathin silver films on silicon oxide and nitride surfaces functionalized with self-assembled monolayers of (3-mercaptopropyl)-trimethoxysilane. First, we compare both solution and vapour-phase functionalization techniques and find the greatest improvement in electrical and optical properties using deposition from solution. Using X-ray photoelectron spectroscopy, we demonstrate that the formation of silver-sulfur covalent bonds is at the root of the improved wetting confirmed by ellipsometry, sheet resistance measurement, and atomic force microscopy. Second, we show that this technique can be extended to functionalize silicon nitride. Finally, we demonstrate a simple, but efficient, low-emissivity optical filter.

  9. Current transport and electroluminescence mechanisms in thin SiO2 films containing Si nanocluster-sensitized erbium ions

    NASA Astrophysics Data System (ADS)

    Jambois, O.; Berencen, Y.; Hijazi, K.; Wojdak, M.; Kenyon, A. J.; Gourbilleau, F.; Rizk, R.; Garrido, B.

    2009-09-01

    We have studied the current transport and electroluminescence properties of metal oxide semiconductor (MOS) devices in which the oxide layer, which is codoped with silicon nanoclusters and erbium ions, is made by magnetron sputtering. Electrical measurements have allowed us to identify a Poole-Frenkel conduction mechanism. We observe an important contribution of the Si nanoclusters to the conduction in silicon oxide films, and no evidence of Fowler-Nordheim tunneling. The results suggest that the electroluminescence of the erbium ions in these layers is generated by energy transfer from the Si nanoparticles. Finally, we report an electroluminescence power efficiency above 10-3%.

  10. Evidence of Silicon Band-Edge Emission Enhancement When Interfaced with SiO2:Er Films

    NASA Astrophysics Data System (ADS)

    Abedrabbo, S.; Fiory, A. T.; Ravindra, N. M.

    2017-02-01

    Nearly two-orders of magnitude increase in room-temperature band-to-band (1.067 eV) infrared emission from crystalline silicon, coated with erbium-doped sol-gel films, have been achieved. Phonon-assisted band-to-band emission from coated and annealed p-Si is strongest for the sample annealed at 700°C. In this paper, evidence of the origin of the emission band from the band edge recombination activities is established. Enhancement of radiative recombination of free carriers is reasoned by stresses at the interface due to the annealed sol-gel-deposited silica. Comparative studies with other strained silicon samples are presented.

  11. The Study of Femtosecond Laser Irradiation on GaAs Solar Cells With TiO2/SiO2 Anti-Reflection Films

    NASA Astrophysics Data System (ADS)

    Hua, Yinqun; Shi, Zhiguo; Wu, Wenhui; Chen, Ruifang; Rong, Zhen; Ye, Yunxia; Liu, Haixia

    Femtosecond laser ablation on GaAs solar cells for space power has been investigated. In particular, we studied the effects of laser energy and laser number on the ablation of solar cells. Furthermore, the morphologies and microstructure of ablation were characterized by the non-contact optical profilometer and scanning electron microscope (SEM). The photovoltaic properties were tested by the volt ampere characteristic test system. The abaltion threshold of the TiO2/SiO2 anti-reflection film of GaAs solar cells was obtained from the linear fit of the dependence of the square diameter of the ablated area with the natural logarithm of the femtosecond laser pulse energy, the resulting threshold of the laser fluence is about 0.31J/cm2, and the corresponding energy is 5.4uJ. The ablation depth showed nonlinear dependence of energy. With the fixed energy 6uJ and the increasing laser number, the damage degree increases obviously. Furthermore, the electric properties also suffer a certain degradation. Among all the evaluated electric properties, the photoelectric conversion efficiency (η) degraded remarkably.

  12. Intensified magneto-resistance by rapid thermal annealing in magnetite (Fe3O4) thin film on SiO2 glass substrate

    NASA Astrophysics Data System (ADS)

    Kobori, H.; Morii, K.; Yamasaki, A.; Sugimura, A.; Taniguchi, T.; Horie, T.; Naitoh, Y.; Shimizu, T.

    2012-12-01

    We have observed large magneto-resistance (MR) intensified by rapid thermal annealing (RTA) in magnetite (Fe3O4) thin film (MTF) on SiO2 glass (a-SiO2) substrate. The MTF was produced by the RF magnetron sputtering method by using a magnetite target. The electrical resistivity (ER) of as-grown MTF (AG-MTF) showed the Mott's variable range hopping behavior, which implies that the AG-MTF is amorphous-like. Although the magneto-resistance (MR) ratio of bulk single crystal is very small except around the Verwey transition temperature (VTT), that of the AG-MTF showed moderately large below room temperature. Due to RTA of the AG-MTF by use of an IR image furnace, the MR ratio of MTFs was intensified, and especially by the annealing around the Curie temperature (585°C) of magnetite. Furthermore the ER of the rapid thermally annealed MTF (RTA-MTF) showed a slight kink at around the VTT, which indicates that the crystallinity of the RTA-MTF is higher than that of the AG-MTF The MTF produced by the RF magnetron sputtering method are composed of magnetite fine particles (MFPs). We consider that the directions of magnetic moments of MFPs in the MTF were spatially randomized by the RTA and the strong spin scattering of itinerant electrons transferring between adjacent MFPs caused the intensification of the MR ratio.

  13. Nonlinear optical properties and surface-plasmon enhanced optical limiting in Ag-Cu nanoclusters co-doped in SiO2 Sol-Gel films

    NASA Astrophysics Data System (ADS)

    Kiran, P. Prem; Shivakiran Bhaktha, B. N.; Rao, D. Narayana; De, Goutam

    2004-12-01

    The nonlinear optical properties and the role of the surface-plasmon resonance (SPR) on optical limiting (OL) properties of Ag -Cu nanoclusters co-doped in SiO2 matrix prepared using the sol-gel technique with a Cu /Ag molar ratio of 1, 2 and 3, respectively, are presented. The studies were made using the second harmonic of high-power nanosecond and picosecond Nd :YAG lasers. These films show a self-defocusing nonlinearity with both nanosecond and picosecond pulses and a good nonlinear absorption behavior with the nanosecond pulse excitation. The nonlinear refractive index decreased with decreasing particle size, whereas the nonlinear absorption increased with an increase in Cu concentration. The observed nonlinear absorption is explained by taking into account the cumulative effect of both the intraband and interband mechanisms. The excitation near the SPR of Cu resulted in an enhanced OL behavior with increasing Cu concentration. No such concentration dependence is observed when the excitation is near the SPR of Ag, however, the limiting threshold is reduced approximately 10-17 times. Excitation at wavelengths far below the SPR of Ag and Cu has not shown any OL behavior. The major contribution toward OL is observed to be from the interband absorption and from a possible energy transfer within the higher unoccupied states of Cu and Ag. Although nonlinear scattering is observed at higher intensities, its contribution is found to be much less than that of the nonlinear absorption assisted by an energy transfer.

  14. Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy

    NASA Astrophysics Data System (ADS)

    Mori, Daichi; Oka, Hiroshi; Hosoi, Takuji; Kawai, Kentaro; Morita, Mizuho; Crumlin, Ethan J.; Liu, Zhi; Watanabe, Heiji; Arima, Kenta

    2016-09-01

    The energy difference between the oxide and bulk peaks in X-ray photoelectron spectroscopy (XPS) spectra was investigated for both GeO2/Ge and SiO2/Si structures with thickness-controlled water films. This was achieved by obtaining XPS spectra at various values of relative humidity (RH) of up to ˜15%. The increase in the energy shift is more significant for thermal GeO2 on Ge than for thermal SiO2 on Si above ˜10-4% RH, which is due to the larger amount of water molecules that infiltrate into the GeO2 film to form hydroxyls. Analyzing the origins of this energy shift, we propose that the positive charging of a partially hydroxylated GeO2 film, which is unrelated to X-ray irradiation, causes the larger energy shift for GeO2/Ge than for SiO2/Si. A possible microscopic mechanism of this intrinsic positive charging is the emission of electrons from adsorbed water species in the suboxide layer of the GeO2 film to the Ge bulk, leaving immobile cations or positively charged states in the oxide. This may be related to the reported negative shift of flat band voltages in metal-oxide-semiconductor diodes with an air-exposed GeO2 layer.

  15. Dry etched SiO2 Mask for HgCdTe Etching Process

    NASA Astrophysics Data System (ADS)

    Chen, Y. Y.; Ye, Z. H.; Sun, C. H.; Deng, L. G.; Zhang, S.; Xing, W.; Hu, X. N.; Ding, R. J.; He, L.

    2016-09-01

    A highly anisotropic etching process with low etch-induced damage is indispensable for advanced HgCdTe (MCT) infrared focal plane array (IRFPA) detectors. The inductively coupled plasma (ICP) enhanced reactive ion etching technique has been widely adopted in manufacturing HgCdTe IRFPA devices. An accurately patterned mask with sharp edges is decisive to accomplish pattern duplication. It has been reported by our group that the SiO2 mask functions well in etching HgCdTe with high selectivity. However, the wet process in defining the SiO2 mask is limited by ambiguous edges and nonuniform patterns. In this report, we patterned SiO2 with a mature ICP etching technique, prior to which a thin ZnS film was deposited by thermal evaporation. The SiO2 film etching can be terminated at the auto-stopping point of the ZnS layer thanks to the high selectivity of SiO2/ZnS in SF6 based etchant. Consequently, MCT etching was directly performed without any other treatment. This mask showed acceptable profile due to the maturity of the SiO2 etching process. The well-defined SiO2 pattern and the etched smooth surfaces were investigated with scanning electron microscopy and atomic force microscope. This new mask process could transfer the patterns exactly with very small etch-bias. A cavity with aspect-ratio (AR) of 1.2 and root mean square roughness of 1.77 nm was achieved first, slightly higher AR of 1.67 was also get with better mask profile. This masking process ensures good uniformity and surely benefits the delineation of shrinking pixels with its high resolution.

  16. [Study on the damage of SiO2 thin films on LiNbO3 crystal in optical parametric oscillator by XRD spectrometry].

    PubMed

    Niu, Rui-Hua; Han, Jing-Hua; Luo, Jin; Lu, Feng; Zhu, Qi-Hua; Li, Tong; Yang, Li-Ming; Feng, Guo-Ying; Zhou, Shou-Huan

    2010-12-01

    In an attempt to elucidate the damage in high transmission thin films on LiNbO3 crystal in optical parametric oscillator, the authors employed XRD spectrometry to investigate the spectrum of laser-induced damage in thin film as well as the morphology of the damage. The authors observed that the damage of thin film was characterized by the depressions/craters in the surface of the films, which were surrounded by a deposition layer with the deceasing thickness from the center of the craters. The XRD measurements indicate that the film was crystallized. The authors analyzed the causes of morphologies and the mechanism of crystallization with the aid of the model for impurity-induced damage in thin solid films. The crystallization was due to the solidification of liquid and gaseous mixtures that result from the strong absorbing to the incident laser. The crater was generated because the mixtures were ejected under the extensive pressure of the laser plasma shock wave. During the process that the mixtures deposit around the craters, the density of the mixtures will decrease and crystallization takes place. As a result, the color of the deposition layer becomes lighter from inside to outside, and the crystallization of the thin film materials was observed by XRD spectrometry.

  17. Large O2 Cluster Ions as Sputter Beam for ToF-SIMS Depth Profiling of Alkali Metals in Thin SiO2 Films.

    PubMed

    Holzer, Sabine; Krivec, Stefan; Kayser, Sven; Zakel, Julia; Hutter, Herbert

    2017-02-21

    A sputter beam, consisting of large O2 clusters, was used to record depth profiles of alkali metal ions (Me(+)) within thin SiO2 layers. The O2 gas cluster ion beam (O2-GCIB) exhibits an erosion rate comparable to the frequently used O2(+) projectiles. However, because of its high sputter yield the necessary beam current is considerably lower (factor 50), resulting in a decreased amount of excess charges at the SiO2 surface. Hence, a reduced electric field is obtained within the remaining dielectric layer. This drastically mitigates the Me(+) migration artifact, commonly observed in depth profiles of various dielectric materials, if analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) in dual beam mode. It is shown, that the application of O2-GCIB results in a negligible residual ion migration for Na(+) and K(+). This enables artifact-free depth profiling with high sensitivity and low operational effort. Furthermore, insight into the migration behavior of Me(+) during O2(+) sputtering is given by switching the sputter beam from O2(+) to O2 clusters and vice versa. K(+) is found to be transported through the SiO2 layer only within the proceeding sputter front. For Na(+) a steadily increasing fraction is observed, which migrates through the unaffected SiO2 layer toward the adjacent Si/SiO2 interface.

  18. Deposition of Thin Film Copper Nanostructures by Electron Beam Physical Vapor Deposition Technique on SiO2/p-TYPE Si(100) and Study of its Oxidation Behavior

    NASA Astrophysics Data System (ADS)

    Yeganeh, M.; Saremi, M.

    Electron beam physical vapor deposition (EBPVD) is being used in coating components for many applications such as for producing nanostructures and integrated circuits (ICs) coating in electronic industry. In this work, copper was deposited on the SiO2/p-type Si(100). Thin film characteristics are investigated by scanning electron microscopy and X-ray diffraction (XRD). Then oxidation behavior of deposits was evaluated by Dektak Surface Profiler and weight gain method at 200 and 300°C. Results showed that thin film copper deposited by EBPVD has better oxidation characteristics in comparison with copper foil.

  19. Statistical study of single and multiple pulse laser-induced damages of HfO2/SiO2 AR coatings at 1064 nm

    NASA Astrophysics Data System (ADS)

    Liu, Wenwen; Wei, Chaoyang; Chen, Shunli; Fang, Zhou; Yi, Kui; Shao, Jianda

    2013-08-01

    Multiple laser irradiations induce a critical issue as regards the lifetime of optical components. HfO2/SiO2 AR coatings for 1064 nm were prepared by conventional electron beam deposition. The evolution of laser-induced damage threshold (LIDT) and 100% damage probability threshold with shot numbers were investigated to illustrate the incubation mechanism of defect-induced damages and the intrinsic material modifications of coatings. It was found that the multi-shot LIDTs were lower than that of single-shot because of "fatigue effect". The 100% damage probability threshold also decreased with increasing shot numbers. This incubation phenomenon implied laser-induced modifications to the coating material that weaken it to subsequent pulse exposures. LID probability curves simulated with a statistical model assuming Gaussian distribution of defect threshold were used to highlight information on defects. Simulation results showed that the thresholds of different kinds of defects decreased with the increase of shot numbers. Optical microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and step profiler were employed in mapping damage morphology features and damage depth to discuss the initiators and mechanism of damage initiation. Additionally, damage regions were accessed by X-ray photoelectron spectroscopy (XPS) to indicate the changes in elemental content and valence of the materials with increasing pulse numbers.

  20. Fracture-induced amorphization of polycrystalline SiO2 stishovite: a potential platform for toughening in ceramics.

    PubMed

    Nishiyama, Norimasa; Wakai, Fumihiro; Ohfuji, Hiroaki; Tamenori, Yusuke; Murata, Hidenobu; Taniguchi, Takashi; Matsushita, Masafumi; Takahashi, Manabu; Kulik, Eleonora; Yoshida, Kimiko; Wada, Kouhei; Bednarcik, Jozef; Irifune, Tetsuo

    2014-10-09

    Silicon dioxide has eight stable crystalline phases at conditions of the Earth's rocky parts. Many metastable phases including amorphous phases have been known, which indicates the presence of large kinetic barriers. As a consequence, some crystalline silica phases transform to amorphous phases by bypassing the liquid via two different pathways. Here we show a new pathway, a fracture-induced amorphization of stishovite that is a high-pressure polymorph. The amorphization accompanies a huge volume expansion of ~100% and occurs in a thin layer whose thickness from the fracture surface is several tens of nanometers. Amorphous silica materials that look like strings or worms were observed on the fracture surfaces. The amount of amorphous silica near the fracture surfaces is positively correlated with indentation fracture toughness. This result indicates that the fracture-induced amorphization causes toughening of stishovite polycrystals. The fracture-induced solid-state amorphization may provide a potential platform for toughening in ceramics.

  1. Electrical behavior of MIS devices based on Si nanoclusters embedded in SiOxNy and SiO2 films

    PubMed Central

    2011-01-01

    We examined and compared the electrical properties of silica (SiO2) and silicon oxynitride (SiOxNy) layers embedding silicon nanoclusters (Sinc) integrated in metal-insulator-semiconductor (MIS) devices. The technique used for the deposition of such layers is the reactive magnetron sputtering of a pure SiO2 target under a mixture of hydrogen/argon plasma in which nitrogen is incorporated in the case of SiOxNy layer. Al/SiOxNy-Sinc/p-Si and Al/SiO2-Sinc/p-Si devices were fabricated and electrically characterized. Results showed a high rectification ratio (>104) for the SiOxNy-based device and a resistive behavior when nitrogen was not incorporating (SiO2-based device). For rectifier devices, the ideality factor depends on the SiOxNy layer thickness. The conduction mechanisms of both MIS diode structures were studied by analyzing thermal and bias dependences of the carriers transport in relation with the nitrogen content. PMID:21711698

  2. Testing Asymmetry in Plasma-Ball Growth Seeded by a Nanoscale Absorbing Defect Embedded in a SiO2 Thin-Film Matrix Subjected to UV Pulsed-Laser Radiation

    SciTech Connect

    Papernov, S.; Schmid, A.W.

    2008-09-16

    Previous studies of ultraviolet, nanosecond-pulsed-laser damage in thin films revealed nanoscale absorbing defects as a major source of damage initiation. It was also demonstrated that damage (crater formation) is facilitated by plasma-ball formation around absorbing defects. In this work an attempt is made to verify the symmetry of the plasma ball by irradiating SiO2 thin film with embedded gold nanoparticles from the side of either the air/film or substrate/film interfaces. Crater-formation thresholds derived in each case support preferential plasma-ball growth in the direction of the laser-beam source. The strong impact of internal E-field distribution is identified.

  3. The FTIR studies of gels and thin films of Al2O3-TiO2 and Al2O3-TiO2-SiO2 systems.

    PubMed

    Adamczyk, Anna; Długoń, Elżbieta

    2012-04-01

    In this work, samples in form of bulk ones and thin films were obtained using the sol-gel method. The bulk samples were heated at different temperatures (500 °C, 850 °C and 1100 °C) corresponding to the annealing process of coatings, deposited on different substrates by dipping and pulling out samples from the proper sol with the stable speed. Thin films of both Al2O3-TiO2 and Al2O3-TiO2-SiO2 systems were deposited on carbon, steel and titanium substrates in two different ways: as single layers obtained from Al2O3 sol, TiO2 sol and Al2O3 sol or deposited as mixed coatings from Al2O3-TiO2 sol as well as Al2O3-TiO2-SiO2 one. All bulk samples were studied by the FTIR spectroscopy and the X-ray diffractometry while thin films were also investigated by the electron microscopy. In the IR spectra of Al2O3-TiO2 samples, as well as gels and coatings, bands due to the vibrations of AlO bonds of the octahedrally and tetrahedrally coordinated aluminum were observed. The IR spectra of samples of Al2O3-TiO2-SiO2 system differ from that of Al2O3-TiO2 ones in presence of bands assigned to the SiO bond vibrations and in positions of bands due to AlO bond vibrations. In all spectra of bulk samples and coatings, the positions of TiO bond vibrations were ascribed basing on the IR spectra of the pure anatase and rutile.

  4. Enhanced and Retarded SiO2 Growth on Thermally Oxidized Fe-Contaminated n-Type Si(001) Surfaces

    NASA Astrophysics Data System (ADS)

    Shimizu, Hirofumi; Hagiwara, Hiroyuki

    2013-04-01

    At the beginning of the oxidation of Fe-contaminated n-type Si(001) surfaces, Fe reacted with oxygen (O2) on the silicon (Si) substrate to form Fe2O3 and oxygen-induced point defects (emitted Si + vacancies). SiO2 growth was mainly enhanced by catalytic action of Fe. At 650 °C, SiO2 growth of the contaminated samples was faster than in reference samples rinsed in RCA solution during the first 60 min. However, it substantially slowed and became less than that of the reference samples. As the oxidation advanced, approximately half of the contaminated Fe atoms became concentrated close to the surface area of the SiO2 film layer. This Fe2O3-rich SiO2 layer acted as a diffusion barrier against oxygen species. The diffusion of oxygen atoms toward the SiO2/Si interface may have been reduced, and in turn, the emission of Si self-interstitials owing to oxidation-induced strain may have been decreased at the SiO2/Si interface, resulting in the retarded oxide growth. These results are evidence that emitted Si self-interstitials are oxidized not in the Fe2O3-rich SiO2 layer, but at the SiO2/Si interface in accordance with a previously proposed model. A possible mechanism based on the interfacial Si emission model is discussed. The activation energies for the oxide growth are found to be in accord with the enhanced and reduced growths of the Fe-contaminated samples.

  5. Time-resolved imaging of material response during laser-induced bulk damage in SiO2

    SciTech Connect

    Demos, S G; Negres, R A

    2008-10-24

    We report on time resolved imaging of the dynamic events taking place during laser-induced damage in the bulk of fused silica samples with nanosecond temporal resolution and one micron spatial resolution. These events include: shock/pressure wave formation and propagation, transient absorption, crack propagation and formation of residual stress fields. The work has been performed using a time-resolved microscope system that utilizes a probe pulse to acquire images at delay times covering the entire timeline of a damage event. Image information is enhanced using polarized illumination and simultaneously recording the two orthogonal polarization image components. For the case of fused silica, an electronic excitation is first observed accompanied by the onset of a pressure wave generation and propagation. Cracks are seen to form early in the process and reach their final size at about 25 ns into the damage event. In addition, changes that in part are attributed to transient absorption in the modified material are observed for delays up to about 200 microseconds.

  6. O atoms loss coefficient on porous SiO2 and TiO2 measured by plasma induced fluorescence

    NASA Astrophysics Data System (ADS)

    Allegraud, Katia; Gatilova, Lina; Guaitella, Olivier; Guillon, Jean; Rousseau, Antoine

    2006-10-01

    The time evolution of O atoms density in the gas phase during the post-discharge of a pulsed plasma is studied using a plasma induced fluorescence technique (PIF): a main long pulse creates the plasma and a shorter one re-excites atoms in the time post-discharge was used. The gas pressure is 133 Pa in N2/O2 mixture and the plasma is a pulsed DC discharge. The surface loss coefficient of O atoms on pyrex, porous silica, porous TiO2 is measured, this latter being a photocatalytic material. It is shown that the presence of porous silica or TiO2 leads to a stong increase of the O atom surface loss coefficient. When nano cluster of TiO2 are deposited on porous silica, the loss coefficient is first high and comparable to the case of the porous silica, but decreases after few milliseconds. Such a decrease of the surface loss coefficient has recently been reported in a pulsed microwave discharge [1]. The effect of the pre-irradiation of the porous materials by external ultraviolet is also studied. [1] G. Cartry, X. Duten and A. Rousseau Plasma Sources Sci. Technol. 15 (2006) 479--488

  7. Densification and residual stress induced by CO2 laser-based mitigation of SiO2 surfaces

    SciTech Connect

    Feit, M D; Matthews, M J; Soules, T F; Stolken, J S

    2010-10-21

    Knowing the ultimate surface morphology resulting from CO{sub 2} laser mitigation of induced laser damage is important both for determining adequate treatment protocols, and for preventing deleterious intensification upon subsequent illumination of downstream optics. Physical effects such as evaporation, viscous flow and densification can strongly affect the final morphology of the treated site. Evaporation is a strong function of temperature and will play a leading role in determining pit shapes when the evaporation rate is large, both because of material loss and redeposition. Viscous motion of the hot molten material during heating and cooling can redistribute material due to surface tension gradients (Marangoni effect) and vapor recoil pressure effects. Less well known, perhaps, is that silica can densify as a result of structural relaxation, to a degree depending on the local thermal history. The specific volume shrinkage due to structural relaxation can be mistaken for material loss due to evaporation. Unlike evaporation, however, local density change can be reversed by post annealing. All of these effects must be taken into account to adequately describe the final morphology and optical properties of single and multiple-pass mitigation protocols. We have investigated, experimentally and theoretically, the significance of such densification on residual stress and under what circumstances it can compete with evaporation in determining the ultimate post treatment surface shape. In general, understanding final surface configurations requires taking all these factors including local structural relaxation densification, and therefore the thermal history, into account. We find that surface depressions due to densification can dominate surface morphology in the non-evaporative regime when peak temperatures are below 2100K.

  8. Novel SiO2/H2Ti2O5·H2O-Nanochain Composite with High UV-Visible Photocatalytic Activity for Supertransparent Multifunctional Thin Films.

    PubMed

    Yao, Lin; He, Junhui; Li, Tong; Ren, Tingting

    2016-12-27

    In the current work, a peroxo titanium complex (PTC) solution was used as a novel water-soluble precursor to fabricate H2Ti2O5·H2O and the SiO2/H2Ti2O5·H2O-nanochain composite at low temperature (90-100 °C). The average width of H2Ti2O5·H2O nanochains is 4.5 ± 1.5 nm. Under full-spectrum irradiation, the Si/Ti-nanochain composite showed good UV-visible light absorption and excellent photocatalytic activity, which is 2.8 times that of P25. In the composite, SiO2 not only contributes to the formation of nanochains and improves the catalytic performance of H2Ti2O5·H2O but also reduces the refractive index of the complex. When coated on transparent organic substrates, the composite thin film exhibited excellent antireflective (as high as 99.3% on PC and 98.9% on PMMA) and self-cleaning properties. Pencil hardness, washing, and tape adhesion tests showed favorable adhesion-to-substrate and mechanical robustness of thin films, which make them extremely attractive for applications as highly transparent and self-cleaning thin films on lenses, photovoltaic cells, and windows of high-rise buildings.

  9. Improved dielectric properties of CaCu3Ti4O12 films with a CaTiO3 interlayer on Pt/TiO2/SiO2/Si substrates prepared by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Lee, Sung-Yun; Kim, Hui Eun; Jo, William; Kim, Young-Hwan; Yoo, Sang-Im

    2015-11-01

    We report the greatly improved dielectric properties of CaCu3Ti4O12 (CCTO) films with a 60 nm-thick CaTiO3 (CTO) interlayer on Pt/TiO2/SiO2/Si substrates. Both CCTO films and CTO interlayers were prepared by pulsed laser deposition (PLD). With increasing the thickness of CCTO from 200 nm to 1.3 μm, the dielectric constants ( ɛ r ) at 10 kHz in both CCTO single-layered and CCTO/CTO double-layered films increased from ˜260 to ˜6000 and from ˜630 to ˜3700, respectively. Compared with CCTO single-layered films, CCTO/CTO double-layered films irrespective of CCTO film thickness exhibited a remarkable decrease in their dielectric losses ( tanδ) (<0.1 at the frequency region of 1 - 100 kHz) and highly reduced leakage current density at room temperature. The reduced leakage currents in CCTO/CTO double-layered films are attributable to relatively higher trap ionization energies in the Poole-Frenkel conduction model. [Figure not available: see fulltext.

  10. Ferroelectric properties of Bi2VO5.5 thin films on LaAlO3 and SiO2/Si substrates with LaNiO3 base electrode

    NASA Astrophysics Data System (ADS)

    Satyalakshmi, K. M.; Varma, K. B. R.; Hegde, M. S.

    1995-07-01

    Ferroelectric bismuth vanadate Bi2VO5.5 (BVO) thin films have been grown on LaAlO3 (LAO) and SiO2/Si substrates with LaNiO3 (LNO) base electrodes by the pulsed laser deposition technique. The effect of substrate temperature on the ferroelectric properties of BVO thin films, has been studied by depositing the thin films at different temperatures. The BVO thin films grown on LNO/LAO were textured whereas the thin films grown on LNO/SiO2/Si were polycrystalline. The BVO thin films grown at 450 °C exhibited good ferroelectric properties indicating that LNO acts as a good electrode material. The remanent polarization Pr and coercive field Ec obtained for the BVO thin films grown at 450 °C on LNO/LAO and LNO/SiO2/Si were 2.5 μC/cm2, 37 kV/cm and 4.6μC/cm2, 93 kV/cm, respectively.

  11. SiO2 Nanoparticule-induced size-dependent genotoxicity - an in vitro study using sister chromatid exchange, micronucleus and comet assay.

    PubMed

    Battal, Dilek; Çelik, Ayla; Güler, Gizem; Aktaş, Ayça; Yildirimcan, Saadet; Ocakoglu, Kasim; Çömelekoǧlu, Ülkü

    2015-04-01

    Fine particles with a characteristic size smaller than 100 nm (i.e. nanoparticlesspread out in nowadays life. Silicon or Si, is one of the most abundant chemical elements found on the Earth. Its oxide forms, such as silicate (SiO4) and silicon dioxide, also known as silica (SiO2), are the main constituents of sand and quartz contributing to 90% of the Earth's crust. In this work, three genotoxicity systems "sister chromatid exchange, cytokinesis block micronucleus test and single cell gel electrophoresis (comet) assay" were employed to provide further insight into the cytotoxic and mutagenic/genotoxic potential of SiO2 nanoparticules (particle size 6 nm, 20 nm, 50 nm) in cultured peripheral blood lymphocytes as in vitro. It was observed that there is a significant decrease in Mitotic index (MI), Cytokinesis block proliferation index (CBPI), proliferation index (PRI) values expressed as Cell Kinetic parameters compared with negative control (p < 0.05). There is a statistically significant difference between negative control culture and culture exposed to SiO2 (6 nm, 20 nm, 50 nm) (p < 0.01, p < 0.01, p < 0.05, respectively). It is found that SiO2 nanoparticles at different size (6, 20, 50 nm) progressively increased the SCE frequency and DNA damage on the basis the AU values compared with negative control (p < 0.05). Results showed that the genotoxic/mutagenic and cytotoxic effects of SiO2 nanoparticules is dependent to particule size.

  12. The correlations of the electronic structure and film growth of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on SiO2.

    PubMed

    Lyu, Lu; Niu, Dongmei; Xie, Haipeng; Zhao, Yuan; Cao, Ningtong; Zhang, Hong; Zhang, Yuhe; Liu, Peng; Gao, Yongli

    2017-01-04

    Combining ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM) and small angle X-ray diffraction (SAXD) measurements, we perform a systematic investigation on the correlations of the electronic structure, film growth and molecular orientation of 2,7-diocty[1]benzothieno[3,2-b]benzothiophene (C8-BTBT) on silicon oxide (SiO2). AFM analysis reveals a phase transition of disorderedly oriented molecules in clusters in thinner films to highly ordered standing-up molecules in islands in thicker films. SAXD peaks consistently support the standing-up configuration in islands. The increasing ordering of the molecular orientation with film thickness contributes to the changing of the shape and lowering of the leading edge of the highest occupied molecular orbital (HOMO). The end methyl of the highly ordered standing molecules forms an outward pointing dipole layer which makes the work function (WF) decrease with increasing thickness. The downward shift of the HOMO and a decrease of WF result in unconventional downward band bending and decreased ionization potential (IP). The correlations of the orientation ordering of molecules, film growth and interface electronic structures provide a useful design strategy to improve the performance of C8-BTBT thin film based field effect transistors.

  13. Preparation and Characterization of SnO2-Nanoparticle-Included Ink Solution and Its Application to the Patterned Pt Films on SiO2/Si Substrates.

    PubMed

    Lee, Su Yeon; Lee, Ho Nyun; Kim, Hyun Jong; Lee, Seong Eui; Lee, Hee Chul

    2015-11-01

    Pure SnO2 nanoparticles with a single tetragonal phase were fabricated and characterized for use as ink solution. It was possible to obtain the SnO2 nanoparticles through the calcination process of SnC204 powders prepared by a hydrothermal reaction of an aqueous solution containing SnCl2 x 2H2O and H2C2O4. The SnO2 powder, synthesized at 600 degrees C, showed a single tetragonal phase, while the powders synthesized at 550 degrees C or lower were composed of a mixture of tetragonal and orthorhombic phases. The particle size of the SnO2 powder with single tetragonal phase was as small as 100 nm and its surface specific area was 12.31 m2/g. It was possible to fabricate the SnO2-nanoparticle-included ink solution for nanoparticle printing by adding a small amount of the previously prepared SnO2 powder to an aqueous solution of glycerol. The region of SnO2 nanoparticles formed by dropping the ink solution was able to successfully fill the gaps between Pt electrodes patterned on SiO2/Si substrates; the range of the gap between the electrodes was from 10 to 100 μm.

  14. High-Mobility Transparent SnO2 and ZnO-SnO2 Thin-Film Transistors with SiO2/Al2O3 Gate Insulators

    NASA Astrophysics Data System (ADS)

    Cheong, Woo-Seok; Yoon, Sung-Min; Hwang, Chi-Sun; Chu, Hye Yong

    2009-04-01

    Using a double-layered gate insulator [SiO2 (100 nm)/Al2O3 (10 nm)] and a dry-etching process for the channel layer, we could obtain high mobility top-gate SnO2 and ZnO-SnO2 (ZTO) transparent thin-film transistor (TTFT). After annealing at 300 °C, for 1 h in O2 ambient, the saturated mobility of SnO2 TTFT was 17.4 cm2 s-1 V-1, and that of ZTO TTFT was 50.4 cm2 s-1 V-1. Generally, both devices operated in the enhancement mode with a drain current on-off ratio of ˜106.

  15. In situ measurement of thickness dependence of magnetoresistance and magnetic hysteresis loops of ultrathin Co films on a SiO 2/Si(1 1 1) substrate

    NASA Astrophysics Data System (ADS)

    Li, M.; Wang, G.-C.

    2000-07-01

    Ultrathin Co films ranging from 1 to 19 monolayers (ML) thick were grown by thermal evaporations on native-oxide-covered Si(1 1 1) surfaces in ultrahigh vacuum (UHV). The thickness-dependent magnetoresistance (MR) and thickness-dependent magnetic hysteresis loops were measured in situ by a collinear four-point probe and surface magneto-optical Kerr effect (SMOKE) techniques, respectively. The magnetoresistance of the Co films, measured with the applied magnetic field parallel to the film plane and perpendicular to the current direction, was obtained only when the Co film thickness reached ˜7 ML. The MR increased monotonically from ˜0.01% at ˜7 ML to ˜0.11% at ˜19 ML. The onset of measurable magnetic hysteresis loops from the Co film occurred at ˜3 ML, earlier than the onset thickness ˜7 ML for measurable MR. The coercivity Hc of the Co film decreased with the film thickness d in the range of 3-19 ML and followed a power law Hc∝ d- n with n=0.33±0.05. The MR change was attributed to scattering from domain walls. The coercivity decrease as a function of thickness was attributed to the decrease of surface domain-wall pinning.

  16. Study of catalytic properties of sol-gel-derived CoO x -SiO2 film systems by the example of the growth of carbon nanomaterials

    NASA Astrophysics Data System (ADS)

    Levitskii, V. S.; Maksimov, A. I.; Moshnikov, V. A.; Terukov, E. I.

    2014-07-01

    Film catalytic samples in the Si-Co-O system in the composition range from 15 to 90 mol % Co have been prepared using the sol-gel technology. Carbon nanomaterials have been fabricated by pyrolytic synthesis using these films as catalysts. Raman spectroscopy of materials has shown that multiwalled carbon nanotubes are formed by pyrolysis on catalytic films containing Co3O4. The dependence of the carbon material length on the synthesis time has been considered. It has been shown that the average growth rate of tubes and fibers is ˜3 μm/min.

  17. Residual stress in Ta2O5-SiO2 composite thin-film rugate filters prepared by radio frequency ion-beam sputtering.

    PubMed

    Tang, Chien-Jen; Jaing, Cheng-Chung; Lee, Kuan-Shiang; Lee, Cheng-Chung

    2008-05-01

    Ta-Si oxide composite thin-film rugate filters were prepared by radio frequency ion-beam sputtering and their residual stress and substrate deflections were measured. The residual stress and substrate deflection of these composite film rugate filters were less than that of notch filters made from a series of discrete quarter-wave layers with alternate high and low indices because of the smooth modulation of composition and no interface structure of the rugate filter.

  18. Effect of ion implantation energy for the synthesis of Ge nanocrystals in SiN films with HfO2/SiO2 stack tunnel dielectrics for memory application

    PubMed Central

    2011-01-01

    Ge nanocrystals (Ge-NCs) embedded in SiN dielectrics with HfO2/SiO2 stack tunnel dielectrics were synthesized by utilizing low-energy (≤5 keV) ion implantation method followed by conventional thermal annealing at 800°C, the key variable being Ge+ ion implantation energy. Two different energies (3 and 5 keV) have been chosen for the evolution of Ge-NCs, which have been found to possess significant changes in structural and chemical properties of the Ge+-implanted dielectric films, and well reflected in the charge storage properties of the Al/SiN/Ge-NC + SiN/HfO2/SiO2/Si metal-insulator-semiconductor (MIS) memory structures. No Ge-NC was detected with a lower implantation energy of 3 keV at a dose of 1.5 × 1016 cm-2, whereas a well-defined 2D-array of nearly spherical and well-separated Ge-NCs within the SiN matrix was observed for the higher-energy-implanted (5 keV) sample for the same implanted dose. The MIS memory structures implanted with 5 keV exhibits better charge storage and retention characteristics compared to the low-energy-implanted sample, indicating that the charge storage is predominantly in Ge-NCs in the memory capacitor. A significant memory window of 3.95 V has been observed under the low operating voltage of ± 6 V with good retention properties, indicating the feasibility of these stack structures for low operating voltage, non-volatile memory devices. PMID:21711708

  19. Growth and structure of water on SiO2 films on Si investigated byKelvin probe microscopy and in situ X-ray Spectroscopies

    SciTech Connect

    Verdaguer, A.; Weis, C.; Oncins, G.; Ketteler, G.; Bluhm, H.; Salmeron, M.

    2007-06-14

    The growth of water on thin SiO{sub 2} films on Si wafers at vapor pressures between 1.5 and 4 torr and temperatures between -10 and 21 C has been studied in situ using Kelvin Probe Microscopy and X-ray photoemission and absorption spectroscopies. From 0 to 75% relative humidity (RH) water adsorbs forming a uniform film 4-5 layers thick. The surface potential increases in that RH range by about 400 mV and remains constant upon further increase of the RH. Above 75% RH the water film grows rapidly, reaching 6-7 monolayers at around 90% RH and forming a macroscopic drop near 100%. The O K-edge near-edge X-ray absorption spectrum around 75% RH is similar to that of liquid water (imperfect H-bonding coordination) at temperatures above 0 C and ice-like below 0 C.

  20. Characterization of phospholipid bilayer formation on a thin film of porous SiO2 by reflective interferometric Fourier transform spectroscopy (RIFTS).

    PubMed

    Pace, Stéphanie; Seantier, Bastien; Belamie, Emmanuel; Lautrédou, Nicole; Sailor, Michael J; Milhiet, Pierre-Emmanuel; Cunin, Frédérique

    2012-05-01

    Classical methods for characterizing supported artificial phospholipid bilayers include imaging techniques such as atomic force microscopy and fluorescence microscopy. The use in the past decade of surface-sensitive methods such as surface plasmon resonance and ellipsometry, and acoustic sensors such as the quartz crystal microbalance, coupled to the imaging methods, have expanded our understanding of the formation mechanisms of phospholipid bilayers. In the present work, reflective interferometric Fourier transform spectrocopy (RIFTS) is employed to monitor the formation of a planar phospholipid bilayer on an oxidized mesoporous Si (pSiO(2)) thin film. The pSiO(2) substrates are prepared as thin films (3 μm thick) with pore dimensions of a few nanometers in diameter by the electrochemical etching of crystalline silicon, and they are passivated with a thin thermal oxide layer. A thin film of mica is used as a control. Interferometric optical measurements are used to quantify the behavior of the phospholipids at the internal (pores) and external surfaces of the substrates. The optical measurements indicate that vesicles initially adsorb to the pSiO(2) surface as a monolayer, followed by vesicle fusion and conversion to a surface-adsorbed lipid bilayer. The timescale of the process is consistent with prior measurements of vesicle fusion onto mica surfaces. Reflectance spectra calculated using a simple double-layer Fabry-Perot interference model verify the experimental results. The method provides a simple, real-time, nondestructive approach to characterizing the growth and evolution of lipid vesicle layers on the surface of an optical thin film.

  1. Visible light-induced hole injection into rectifying molecular wires anchored on Co3O4 and SiO2 nanoparticles.

    PubMed

    Soo, Han Sen; Agiral, Anil; Bachmeier, Andreas; Frei, Heinz

    2012-10-17

    Tight control of charge transport from a visible light sensitizer to a metal oxide nanoparticle catalyst for water oxidation is a critical requirement for developing efficient artificial photosynthetic systems. By utilizing covalently anchored molecular wires for hole transport from sensitizer to the oxide surface, the challenge of high rate and unidirectionality of the charge flow can be addressed. Functionalized hole conducting molecular wires of type p-oligo(phenylenevinylene) (3 aryl units, abbreviated PV3) with various anchoring groups for the covalent attachment to Co(3)O(4) catalyst nanoparticles were synthesized and two alternative methods for attachment to the oxide nanoparticle surface introduced. Covalent anchoring of intact PV3 molecules on Co(3)O(4) nanoparticles (and on SiO(2) nanoparticles for control purposes) was established by FT-Raman, FT-IR, and optical spectroscopy including observation, in some cases, of the vibrational signature of the anchored functionality. Direct monitoring of the kinetics of hole transfer from a visible light sensitizer in aqueous solution ([Ru(bpy)(3)](2+) (and derivatives) light absorber, [Co(NH(3))(5)Cl](2+) acceptor) to wire molecules on inert SiO(2)(12 nm) particles by nanosecond laser absorption spectroscopy revealed efficient, encounter controlled rates. For wire molecules anchored on Co(3)O(4) nanoparticles, the recovery of the reduced sensitizer at 470 nm indicated similarly efficient hole transfer to the attached PV3, yet no transient hole signal was detected at 600 nm. This implies hole injection from the anchored wire molecule into the Co(3)O(4) particle within 1 μs or shorter, indicating efficient charge transport from the visible light sensitizer to the oxide catalyst particle.

  2. Shear strength of metal - SiO2 contacts

    NASA Technical Reports Server (NTRS)

    Pepper, S. V.

    1978-01-01

    The strength of the bond between metals and SiO2 was studied by measuring the static coefficient of friction of metals contacting alpha-quartz in ultrahigh vacuum. It was found that copper with either chemisorbed oxygen, nitrogen, or sulphur exhibited higher contact strength on stoichiometric SiO2 than did clean copper. Since the surface density of states induced by these species on copper is similar, it appears that the strength of the interfacial bond can be related to the density of states on the metal surface.

  3. Investigation of the structure and composition of film sol-gel-derived CoO x -SiO2 systems

    NASA Astrophysics Data System (ADS)

    Levitskii, V. S.; Maksimov, A. I.; Moshnikov, V. A.; Terukov, E. I.

    2014-02-01

    Samples of Si-Co-O ranging in composition from 15 to 90% of cobalt content have been synthesized by the sol-gel technology. The results of atomic force microscopy have demonstrated that the preliminary centrifugation of the solutions makes it possible to control the size of the nanospheres obtained in the stage of sol formation. For diagnostics of the phase composition of the film and bulk materials, Raman spectroscopy and X-ray powder diffraction analysis have been used. The results of X-ray powder diffraction analysis and Raman spectroscopy have revealed that the nanospheres belong to the Co3O4 spinel phase. It has been found that there is a correlation between the positions of the Raman band maxima and the nanosphere size.

  4. Vacuum ultraviolet thin films. I - Optical constants of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 thin films. II - Vacuum ultraviolet all-dielectric narrowband filters

    NASA Technical Reports Server (NTRS)

    Zukic, Muamer; Torr, Douglas G.; Spann, James F.; Torr, Marsha R.

    1990-01-01

    An iteration process matching calculated and measured reflectance and transmittance values in the 120-230 nm VUV region is presently used to ascertain the optical constants of bulk MgF2, as well as films of BaF2, CaF2, LaF3, MgF2, Al2O3, HfO2, and SiO2 deposited on MgF2 substrates. In the second part of this work, a design concept is demonstrated for two filters, employing rapidly changing extinction coefficients, centered at 135 nm for BaF2 and 141 nm for SiO2. These filters are shown to yield excellent narrowband spectral performance in combination with narrowband reflection filters.

  5. Fabrication of noble-metal nanoparticle-doped SiO2-B2O3-P2O5 waveguide films

    NASA Astrophysics Data System (ADS)

    Lee, Hunhyeong; Kang, Minkyung; Nichols, William T.; Shin, Dongwook

    2012-05-01

    In this article, we report the fabrication and the characterization of Pt/SiO2-B2O3-P2O5 and Au/SiO2-B2O3-P2O5 composite thin films suitable for planar lightwave circuits (PLCs). The host material was prepared by using flame hydrolysis deposition (FHD). Platinum was doped from colloidal solutions with concentrations of 500, 1000, and 2000 ppm. Gold was doped by sputtering with various deposition times. The samples displayed absorption peaks originating from the surface plasmon resonance (SPR) of the dopant metal particles. With increasing dopant particle size, the absorption peak shifted toward longer wavelength, and the full width at half maximum (FWHM) of the absorption band broadened. The Maxwell-Garnett theory was used to explain the size dependence of the plasmon peaks. The dopant metal particles were found to order as a monolayer within the silica matrix, opening the possibility for surface-plasmon-resonance-based waveguiding in optical devices.

  6. Simultaneous electroanalytical determination of hydroquinone and catechol in the presence of resorcinol at an SiO2/C electrode spin-coated with a thin film of Nb2O5.

    PubMed

    Canevari, Thiago C; Arenas, Leliz T; Landers, Richard; Custodio, Rogério; Gushikem, Yoshitaka

    2013-01-07

    This paper describes the development, characterization and application of an Nb(2)O(5) film formed on the surface of a carbon ceramic material, SiO(2)/C, obtained by a sol-gel method, using the spin-coating technique. The working electrode using this material will be designated as SiCNb. Hydroquinone and catechol can be oxidized at this electrode in the presence of resorcinol, allowing their simultaneous detection. The electrochemical properties of the resulting electrode were investigated using cyclic and differential pulse voltammetry techniques. Well-defined and separated oxidation peaks were observed by differential pulse voltammetry in Tris-HCl buffer solution at pH 7 containing 1 mol L(-1) KCl in the supporting electrolyte solution. The SiCNb electrode exhibited high sensitivity in the simultaneous determination of hydroquinone and catechol in the presence of resorcinol, with the limits of detection for hydroquinone and catechol being 1.6 μmol L(-1) and 0.8 μmol L(-1), respectively. Theoretical calculations were performed to determine the ionization energies of hydroquinone, catechol and resorcinol; the results were used to explain the simultaneous determination of species by differential pulse voltammetry. The presence of resorcinol did not produce any interference in the simultaneous detection of hydroquinone and catechol on the surface of the modified electrode.

  7. Semiconducting electronic property of graphene adsorbed on (0001) surfaces of SiO2.

    PubMed

    Nguyen, Thanh Cuong; Otani, Minoru; Okada, Susumu

    2011-03-11

    First-principles total energy calculations are performed to investigate the energetics and electronic structures of graphene adsorbed on both an oxygen-terminated SiO2 (0001) surface and a fully hydroxylated SiO2 (0001) surface. We find that there are several stable adsorption sites for graphene on both O-terminated and hydroxylated SiO2 surfaces. The binding energy in the most stable geometry is found to be 15 meV per C atom, indicating a weak interaction between graphene and SiO2 (0001) surfaces. We also find that the graphene adsorbed on SiO2 is a semiconductor irrespective of the adsorption arrangement due to the variation of on-site energy induced by the SiO2 substrate.

  8. Effect of surface wettability properties on the electrical properties of printed carbon nanotube thin-film transistors on SiO2/Si substrates.

    PubMed

    Liu, Zhen; Zhao, Jianwen; Xu, Wenya; Qian, Long; Nie, Shuhong; Cui, Zheng

    2014-07-09

    The precise placement and efficient deposition of semiconducting single-walled carbon nanotubes (sc-SWCNTs) on substrates are challenges for achieving printed high-performance SWCNT thin-film transistors (TFTs) with independent gates. It was found that the wettability of the substrate played a key role in the electrical properties of TFTs for sc-SWCNTs sorted by poly[(9,9-dioctylfluorene-2,7-diyl)-co-(1,4-benzo-2,1,3-thiadiazole)] (PFO-BT). In the present work we report a simple and scalable method which can rapidly and selectively deposit a high concentration of sc-SWCNTs in TFT channels by aerosol-jet-printing. The method is based on oxygen plasma treatment of substrates, which tunes the surface wettability. TFTs printed on the treated substrates demonstrated a low operation voltage, small hysteresis, high mobility up to 32.3 cm(2) V(-1) s(-1), and high on/off ratio up to 10(6) after only two printings. Their mobilities were 10 and 30 times higher than those of TFTs fabricated on untreated and low-wettability substrates. The uniformity of printed TFTs was also greatly improved. Inverters were constructed by printed top-gate TFTs, and a maximum voltage gain of 17 at Vdd = 5 V was achieved. The mechanism of such improvements is that the PFO-BT-functionalized sc-SWCNTs are preferably immobilized on the oxygen plasma treated substrates due to the strong hydrogen bonds between sc-SWCNTs and hydroxyl groups on the substrates.

  9. Crack suppression of silica glass formed by zoned F2 laser-induced photochemical surface modification of hard silicone thin film coating on polycarbonate

    NASA Astrophysics Data System (ADS)

    Nojiri, Hidetoshi; Okoshi, Masayuki

    2016-12-01

    The surface layer of a hard silicone thin film coating on polycarbonate was modified to silica glass (SiO2) through F2-laser-induced photochemical reactions. To obtain samples with higher abrasion resistances, SiO2 films of 1 µm thickness and over were successfully formed without cracking, by zoning the laser-irradiated area of micrometer order. With the conversion of silicone to SiO2, the volumetric shrinkage of the sample was induced, which simply depended on the number of photons, by varying the single-pulse fluence and irradiation time of a F2 laser. The ratio of volumetric shrinkage to the original silicone was estimated to be approximately 0.85, generating tensile stress in SiO2. The stress could be suppressed to be lower than 48 MPa for typical SiO2 by reducing the laser-irradiated area to be of micrometer order. Also, when the length of one side of the irradiated area is 1 mm, the thickness of the SiO2 film is expected to increase to approximately 5 µm.

  10. 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.

  11. Competing liquid phase instabilities during pulsed laser induced self-assembly of copper rings into ordered nanoparticle arrays on SiO2

    SciTech Connect

    Wu, Yeuyeng; Fowlkes, Jason Davidson; Kondic, Lou; Diez, Javier A; Gonzalez, Alejandro; Roberts, Nicholas A

    2011-01-01

    Nanoscale copper rings of different radii, thicknesses, and widths were synthesized on silicon dioxide thin films and were subsequently liquefied via a nanosecond pulse laser treatment. During the nanoscale liquid lifetimes, the rings experience competing retraction dynamics and thin film and/or Rayleigh-Plateau types of instabilities, which lead to arrays of ordered nanodroplets. Surprisingly, the results are significantly different from those of similar experiments carried out on a Si surface.(1) We use hydrodynamic simulations to elucidate how the different liquid/solid interactions control the different instability mechanisms in the present problem.

  12. Light harvesting with Ge quantum dots embedded in SiO2 or Si3N4

    NASA Astrophysics Data System (ADS)

    Cosentino, Salvatore; Sungur Ozen, Emel; Raciti, Rosario; Mio, Antonio M.; Nicotra, Giuseppe; Simone, Francesca; Crupi, Isodiana; Turan, Rasit; Terrasi, Antonio; Aydinli, Atilla; Mirabella, Salvo

    2014-01-01

    Germanium quantum dots (QDs) embedded in SiO2 or in Si3N4 have been studied for light harvesting purposes. SiGeO or SiGeN thin films, produced by plasma enhanced chemical vapor deposition, have been annealed up to 850 °C to induce Ge QD precipitation in Si based matrices. By varying the Ge content, the QD diameter can be tuned in the 3-9 nm range in the SiO2 matrix, or in the 1-2 nm range in the Si3N4 matrix, as measured by transmission electron microscopy. Thus, Si3N4 matrix hosts Ge QDs at higher density and more closely spaced than SiO2 matrix. Raman spectroscopy revealed a higher threshold for amorphous-to-crystalline transition for Ge QDs embedded in Si3N4 matrix in comparison with those in the SiO2 host. Light absorption by Ge QDs is shown to be more effective in Si3N4 matrix, due to the optical bandgap (0.9-1.6 eV) being lower than in SiO2 matrix (1.2-2.2 eV). Significant photoresponse with a large measured internal quantum efficiency has been observed for Ge QDs in Si3N4 matrix when they are used as a sensitive layer in a photodetector device. These data will be presented and discussed, opening new routes for application of Ge QDs in light harvesting devices.

  13. SAW-grade SiO2 for advanced microfluidic devices

    NASA Astrophysics Data System (ADS)

    Winkler, Andreas; Menzel, Siegfried; Schmidt, Hagen

    2009-05-01

    Acoustoelectronic devices based on surface acoustic wave (SAW) technology are primarily used in radio frequency filters, delay lines, duplexers, amplifiers and RFID tags. Thereby, SAW's are excited at the surface of piezoelectric materials (e.g. Quartz, LiTaO3, LiNbO3) by an RF signal applied via interdigital transducers (IDTs)1. Novel SAW applications that emerged recently in the field of microfluidics such as the handling of minimum quantities of fluids or gases2,3 require a fluid compatible design approach, high power durability and long lifetime of the devices. However, conventional SAW devices with finger electrodes arranged on top of the chip surface experience acoustomigration damage4,5 at high power input and/or higher operating temperature leading to failure of the device. Additionally, inappropriate material systems or chip surface topography can limit their performance in microfluidic application. To overcome these limitations the electrodes can be buried in an acoustically suited ("SAW-grade") functional layer which moreover should be adjustable to the specific biotechnological task. Depending on the properties of this layer, it can suppress the acoustomigration impact6 and improve the power durability of the device. Also, a reduction of the thermally-induced frequency shift is possible7. The present paper describes a novel SAW based chip technology approach using a modular concept. Here, the electrodes are buried in surface polished SAW-grade SiO2 fabricated by means of reactive RF magnetron sputtering from a SiO2- target. This approach will be demonstrated for two different metallization systems based on Al or Cu thin films on 128° YX-LiNbO3 substrates. We also show the application of the SiO2-layer with respect to compensation of thermallyinduced frequency shift and bio /chemical surface modification. Investigations were carried out using atomic force microscopy, laser-pulse acoustic measurement, glow-discharge optical emission spectroscopy

  14. Negative photoconductance in SiO2(Co)/GaAs heterostructure in the avalanche regime

    NASA Astrophysics Data System (ADS)

    Lutsev, L. V.; Pavlov, V. V.; Usachev, P. A.; Astretsov, A. A.; Stognij, A. I.; Novitskii, N. N.

    2012-12-01

    Negative photoconductance of heterostructures of silicon dioxide films containing cobalt nanoparticles grown on gallium arsenide SiO2(Co)/GaAs has been observed in the avalanche regime. Light with the photon energy less than the bandgap energy of the GaAs creates holes trapped on defects within the GaAs bandgap. This suppresses the avalanche feedback and causes a reduction of the current flowing through the SiO2(Co)/GaAs heterostructure.

  15. Physical origins of mobility degradation in extremely scaled SiO2/HfO2 gate stacks with La and Al induced dipoles

    NASA Astrophysics Data System (ADS)

    Ando, Takashi; Copel, Matt; Bruley, John; Frank, Martin M.; Watanabe, Heiji; Narayanan, Vijay

    2010-03-01

    We demonstrate metal-gate-induced interfacial layer (IL) scaling using a HfO2 dielectric and clarify the kinetics underlying this process. The intrinsic IL scaling effect on electron mobility is separated from La and Al-induced dipole effects. We find that the mobility degradation for La-containing high-κ dielectrics is not due to the La-induced dipole but due to the intrinsic IL scaling effect, whereas the Al-induced dipole brings about additional mobility degradation. This unique nature of the La-induced dipole enables aggressive equivalent oxide thickness scaling down to 0.42 nm without extrinsic mobility degradation when combined with IL scaling.

  16. Fabrication of SiO2/c-Si/SiO2 Double Barrier Structure Using Lateral Solid Phase Epitaxy

    NASA Astrophysics Data System (ADS)

    Novikov, S. V.; Sinkkonen, J.

    Formation of an ultra-thin-film silicon-on-insulator structure by lateral solid state epitaxy (LSPE) of amorphous Si on SiO2 has been investigated. The LSPE growth length was found. The SiO2/Si/SiO2 double barrier structure with single crystalline silicon well has been grown.

  17. Nonlithographic SiO2 Nanodot Arrays via Template Synthesis Approach

    NASA Astrophysics Data System (ADS)

    Cha, Young Kwan; Seo, David; Yoo, In K.; Park, Sangjin; Jeong, Soo-Hwan; Chung, Chee Won

    2004-08-01

    We present a method for fabricating SiO2 nanodot arrays through pattern transfer of self-organized tantalum oxide hard masks on to a Si wafer. Tantalum oxide nanopillar arrays are formed at the bottom of anodic aluminum oxide by electrochemical anodization of the Al/Ta films on a Si wafer. Then the tantalum oxide nanopillars were used as hard masks for formation of SiO2 nanostructures. Ion milling was used for the pattern transfer. The density and diameter of the SiO2 nanodot arrays could be controlled by varing the anodizing conditions. The average diameters and areal density of prepared SiO2 nanodisks were 68 nm and 1010/cm2, respectively. Through this approach, it is expected that a wide variety of nanodisk arrays over large areas can be prepared.

  18. Shock induced reaction in Chicxulub target materials (CaSO4 and SiO2) and their relation to extinctions

    NASA Astrophysics Data System (ADS)

    Chen, Guangqing; Ahrens, Thomas J.

    1993-03-01

    The global platinum element rich layer, the presence of shocked quartz grains (in some cases with stishovite), and the observation of a tektite-rich layer, precisely at the K-T boundary, are the three major arguments for the extinction bolide impact hypothesis of Alvarez et al. Tektites (spherules) from Beloc in Haiti and Mimbral in Mexico received particular interest because of their geological proximity to the Chicxulub impact structure, which is a leading candidate for at least one of the K-T impact craters. Although in most localities the original glass has weathered to clay minerals, some shock-induced glass is found in outcrops and drill cores which is used for Ar-38/Ar-39 dating. The glassy tektites were found to be chemically similar and coeval at 65.0 Ma with Chicxulub melt rock. Two kinds of K-T spherules were discovered: (1) a silic black glass; and (2) a yellow glass, enriched in Ca, Mg, and S. The high sulfur content of the glass and the abundance of anhydrite (CaSO4) in the carbonate-evaporite sequence observed in Drill Holes Y-1 and Y-2 at Chicxulub prompted studies of calcium sulfate devolatization. Further discussion of our experiments is presented.

  19. Light Induced Water Oxidation on Cobalt-Phosphate (Co-Pi) Catalyst Modified Semi-Transparent, Porous SiO2-BiVO4 Electrodes

    SciTech Connect

    Pilli, S. K.; Deutsch, T. G.; Furtak, T. E.; Turner, J. A.; Brown, L. D.; Herring, A. M.

    2012-04-21

    A facile and simple procedure for the synthesis of semi-transparent and porous SiO{sub 2}-BiVO{sub 4} electrodes is reported. The method involves a surfactant assisted metal-organic decomposition at 500 C. An earth abundant oxygen evolution catalyst (OEC), cobalt phosphate (Co-Pi), has been used to modify the SiO{sub 2}-BiVO{sub 4} electrode by electrodeposition (ED) and photoassisted electrodeposition (PED) methods. Modified electrodes by these two methods have been examined for light induced water oxidation and compared to the unmodified SiO{sub 2}-BiVO{sub 4} electrodes by various photoelectrochemical techniques. The PED method was a more effective method of OEC preparation than the ED method as evidenced by an increased photocurrent magnitude during photocurrent-potential (I-V) characterizations. Electrode surfaces catalyzed by PED exhibited a very large cathodic shift (420 mV) in the onset potential for water oxidation. The chopped-light I-V measurements performed at different intervals over 24-hour extended testing under illumination and applied bias conditions show a fair photostability for PED Co-Pi modified SiO{sub 2}-BiVO{sub 4}.

  20. In-situ luminescence monitoring of ion-induced damage evolution in SiO2 and Al2O3

    DOE PAGES

    Crespillo, Miguel L.; Graham, Joseph T.; Zhang, Yanwen; ...

    2015-12-17

    Real-time, in-situ ionoluminescence measurements provide information of evolution of emission bands with ion fluence, and thereby establish a correlation between point defect kinetics and phase stability. Using fast light ions (2 MeV H and 3.5 He MeV) and medium mass-high energy ions (8 MeV O, E=0.5 MeV/amu), scintillation materials of a-SiO2, crystalline quartz, and Al2O3 are comparatively investigated at room temperature with the aim of obtaining a further insight on the structural defects induced by ion irradiation and understand the role of electronic energy loss on the damage processes. For more energetic heavy ions, the electronic energy deposition pattern offersmore » higher rates of excitation deeper into the material and allows to evaluate the competing mechanisms between the radiative and non-radiative de-excitation processes. Irradiations with 8 MeV O ions have been selected corresponding to the electronic stopping regime, where the electronic stopping power is dominant, and above the critical amorphization threshold for quartz. Lastly, the usefulness of IBIL and its specific capabilities as a sensitive tool to investigate the material characterization and evaluation of radiation effects are demonstrated.« less

  1. Hard-Mask-Through UV-Light-Induced Damage to Low-k Film during Plasma Process for Dual Damascene

    NASA Astrophysics Data System (ADS)

    Noriaki Matsunaga,; Hirokatsu Okumura,; Butsurin Jinnai,; Seiji Samukawa,

    2010-04-01

    Plasma irradiation impact on a SiO2-hardmask/SiOCH low-k film stacked structure was investigated in detail. The plasma irradiation induces damage to the low-k film although it is covered by a hard mask. The hard-mask-through UV-light-induced damage showed plasma source gas dependence. The damage is determined by the UV light wavelength and photon energy. It was also found that a high substrate temperature accelerates the hard-mask-through UV-light-induced damage. The hard-mask-through UV-light-induced damage was hardly seen for the hard masks thicker than 115 nm in the O2-irradiation experiment. Conversely, an actual SiO2 film deposition process by plasma-enhanced chemical vapor deposition (PE-CVD) induces damage during deposition. The PE-CVD process induces heavier damage to the low-k film than the O2-plasma experiment. Higher process temperature accelerates the hard-mask-through UV-light-induced damage in the hard mask SiO2 deposition process.

  2. Thermal Investigation of SiO2-Bi2O3 Heavy Metal Glasses

    NASA Astrophysics Data System (ADS)

    Simon, V.; Todea, M.; Simon, S.

    Structural changes induced by temperature rising in binary silico-bismuthate glasses are investigated by differential thermal analysis. Several exothermic peaks are recorded for all samples. Progressive substitution of Bi2O3 by SiO2 contributes to the structural relaxation of vitreous network and leads to diminishing of the melting temperature, even as SiO2 content reaches 40 mol%. Glass stability is enhanced by addition of silicon dioxide.

  3. Dielectric properties of (110) oriented PbZrO3 and La-modified PbZrO3 thin films grown by sol-gel process on Pt(111)/Ti /SiO2/Si substrate

    NASA Astrophysics Data System (ADS)

    Parui, Jayanta; Krupanidhi, S. B.

    2006-08-01

    Highly (110) preferred orientated antiferroelectric PbZrO3 (PZ) and La-modified PZ thin films have been fabricated on Pt /Ti/SiO2/Si substrates using sol-gel process. Dielectric properties, electric field induced ferroelectric polarization, and the temperature dependence of the dielectric response have been explored as a function of composition. The Tc has been observed to decrease by ˜ 17°C per 1mol% of La doping. Double hysteresis loops were seen with zero remnant polarization and with coercive fields in between 176 and 193kV/cm at 80°C for antiferroelectric to ferroelectric phase transformation. These slim loops have been explained by the high orientation of the films along the polar direction of the antiparallel dipoles of a tetragonal primitive cell and by the strong electrostatic interaction between La ions and oxygen ions in an ABO3 perovskite unit cell. High quality films exhibited very low loss factor less than 0.015 at room temperature and pure PZ; 1 and 2mol% La doped PZs have shown the room temperature dielectric constant of 135, 219, and 142 at the frequency of 10kHz. The passive layer effects in these films have been explained by Curie constants and Curie temperatures. The ac conductivity and the corresponding Arrhenius plots have been shown and explained in terms of doping effect and electrode resistance.

  4. Interaction of tetraethoxysilane with OH-terminated SiO2 (0 0 1) surface: A first principles study

    NASA Astrophysics Data System (ADS)

    Deng, Xiaodi; Song, Yixu; Li, Jinchun; Pu, Yikang

    2014-06-01

    First principles calculates have been performed to investigate the surface reaction mechanism of tetraethoxysilane (TEOS) with fully hydroxylated SiO2(0 0 1) substrate. In semiconductor industry, this is the key step to understand and control the SiO2 film growth in chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes. During the calculation, we proposed a model which breaks the surface dissociative chemisorption into two steps and we calculated the activation barriers and thermochemical energies for each step. Our calculation result for step one shows that the first half reaction is thermodynamically favorable. For the second half reaction, we systematically studied the two potential reaction pathways. The comparing result indicates that the pathway which is more energetically favorable will lead to formation of crystalline SiO2 films while the other will lead to formation of disordered SiO2 films.

  5. Optical properties of the Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings

    NASA Astrophysics Data System (ADS)

    Marszałek, Konstanty; Winkowski, Paweł; Jaglarz, Janusz

    2014-01-01

    Investigations of bilayer and trilayer Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10-3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al2O3, 0.6 nm - 0.8 nm/s for HfO2 and 0.6 nm/s for SiO2. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al2O3/SiO2 and 78 nm/156 nm/78 nm for Al2O3/HfO2/SiO2. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.

  6. Laser-induced chemical vapour deposition of conductive and insulating thin films

    NASA Astrophysics Data System (ADS)

    Reisse, G.; Gaensicke, F.; Ebert, R.; Illmann, U.; Johansen, H.

    1992-01-01

    Investigations concerning the laser-induced chemical vapour deposition of Mo, W, Co and TiSi 2 conductive thin film structures from Mo(CO) 6, W(CO) 6, Co 2(CO) 8, TiCl 4 and SiH 4 using a direct writing method are presented. SiO 2 thin films were deposited from SiH 4 and N 2O in a large area deposition process stimulated by an excimer laser by using a parallel beam configuration.

  7. Magnetoelectric coupling in Tb0.3Dy0.7Fe2/Pt/PbZr0.56Ti0.44O3 thin films deposited on Pt/TiO2/SiO2/Si substrate

    NASA Astrophysics Data System (ADS)

    Cibert, C.; Zhu, J.; Poullain, G.; Bouregba, R.; More-Chevalier, J.; Pautrat, A.

    2013-01-01

    Tb0.3Dy0.7Fe2/Pt/PbZr0.56Ti0.44O3 (Terfenol-D/Pt/PZT) thin films were sputtered on Pt/TiO2/SiO2/Si substrate. PZT and Terfenol-D layers were chosen for their large piezoelectric and magnetostrictive coefficients, respectively. 4%-5% magnetocapacitance has been measured on a Terfenol-D/Pt/PZT stack at room temperature. A magnetoelectric (ME) voltage coefficient of 150 mV/cm Oe was obtained at low dc magnetic field out of mechanical resonance. This work demonstrates the possibility to achieve ME effect in integrated devices involving Terfenol-D and PZT thin films providing that the diffusion, which may occur between both active layers is reduced using an intermediate layer.

  8. Optical properties of self-assembled TiO2-SiO2 double-layered photonic crystals.

    PubMed

    Oh, Yong Taeg; Koo, Bo Ra; Shin, Dong Chan

    2013-01-01

    The optical properties of self-assembled TiO2/SiO2 double-layered photonic crystals were examined using SiO2 and TiO2 nanopowders. The SiO2 and TiO2 nanopowders were fabricated using the well-known Stöber process, and the double-layered structure was self-assembled by an evaporation method. Self-assembled TiO2 thin film was coated at a 1.2 mm thickness by the evaporation process, and 3 atomic layers of the SiO2 layer was coated onto the TiO2 thin film. The relative reflectance peak intensity of the photonic bandgap in the specimen was 13% before thermal treatment. The peak value was increased by sequential heat-treatments and reached the highest value of 21% at 400 degrees C.

  9. Determination of the SiO(2)/Si interface roughness by diffuse reflectance measurements.

    PubMed

    Roos, A; Bergkvist, M; Ribbing, C G

    1988-11-15

    The problem of determining the roughness of the SiO(2)/Si interface is treated. A model is used based on the Fresnel formalism and scalar scattering theory. The resulting formulas express the diffuse reflectance as a function of the optical constants of the two materials, the oxide thickness and the rms roughness of the interfaces. Using the roughness values as adjustable parameters, quantitative information about the interface roughness is obtained from the diffuse reflectance spectra for an SiO(2)/Si double layer. Excellent agreement between calculated and experimental spectra is obtained for an rms roughness of 9.0 nm at the front surface and 2.2 nm at the oxide substrate interface for the case of a low-pressure low-temperature CVD film of SiO(2) on Si.

  10. Determination of the SiO(2)/Si interface roughness by diffuse reflectance measurements.

    PubMed

    Roos, A; Bergkvist, M; Ribbing, C G

    1988-10-15

    The problem of determining the roughness of the SiO(2)/Si interface is treated. A model is used based on the Fresnel formalism and scalar scattering theory. The resulting formulas express the diffuse reflectance as a function of the optical constants of the two materials, the oxide thickness and the rms roughness of the interfaces. Using the roughness values as adjustable parameters, quantitative information about the interface roughness is obtained from the diffuse reflectance spectra for an SiO(2)/Si double layer. Excellent agreement between calculated and experimental spectra is obtained for an rms roughness of 9.0 nm at the front surface and 2.2 nm at the oxide substrate interface for the case of a low-pressure low-temperature CVD film of SiO(2) on Si.

  11. Transfer free graphene growth on SiO2 substrate at 250 °C.

    PubMed

    Vishwakarma, Riteshkumar; Rosmi, Mohamad Saufi; Takahashi, Kazunari; Wakamatsu, Yuji; Yaakob, Yazid; Araby, Mona Ibrahim; Kalita, Golap; Kitazawa, Masashi; Tanemura, Masaki

    2017-03-02

    Low-temperature growth, as well as the transfer free growth on substrates, is the major concern of graphene research for its practical applications. Here we propose a simple method to achieve the transfer free graphene growth on SiO2 covered Si (SiO2/Si) substrate at 250 °C based on a solid-liquid-solid reaction. The key to this approach is the catalyst metal, which is not popular for graphene growth by chemical vapor deposition. A catalyst metal film of 500 nm thick was deposited onto an amorphous C (50 nm thick) coated SiO2/Si substrate. The sample was then annealed at 250 °C under vacuum condition. Raman spectra measured after the removal of the catalyst by chemical etching showed intense G and 2D peaks together with a small D and intense SiO2 related peaks, confirming the transfer free growth of multilayer graphene on SiO2/Si. The domain size of the graphene confirmed by optical microscope and atomic force microscope was about 5 μm in an average. Thus, this approach will open up a new route for transfer free graphene growth at low temperatures.

  12. Transfer free graphene growth on SiO2 substrate at 250 °C

    NASA Astrophysics Data System (ADS)

    Vishwakarma, Riteshkumar; Rosmi, Mohamad Saufi; Takahashi, Kazunari; Wakamatsu, Yuji; Yaakob, Yazid; Araby, Mona Ibrahim; Kalita, Golap; Kitazawa, Masashi; Tanemura, Masaki

    2017-03-01

    Low-temperature growth, as well as the transfer free growth on substrates, is the major concern of graphene research for its practical applications. Here we propose a simple method to achieve the transfer free graphene growth on SiO2 covered Si (SiO2/Si) substrate at 250 °C based on a solid-liquid-solid reaction. The key to this approach is the catalyst metal, which is not popular for graphene growth by chemical vapor deposition. A catalyst metal film of 500 nm thick was deposited onto an amorphous C (50 nm thick) coated SiO2/Si substrate. The sample was then annealed at 250 °C under vacuum condition. Raman spectra measured after the removal of the catalyst by chemical etching showed intense G and 2D peaks together with a small D and intense SiO2 related peaks, confirming the transfer free growth of multilayer graphene on SiO2/Si. The domain size of the graphene confirmed by optical microscope and atomic force microscope was about 5 μm in an average. Thus, this approach will open up a new route for transfer free graphene growth at low temperatures.

  13. Transfer free graphene growth on SiO2 substrate at 250 °C

    PubMed Central

    Vishwakarma, Riteshkumar; Rosmi, Mohamad Saufi; Takahashi, Kazunari; Wakamatsu, Yuji; Yaakob, Yazid; Araby, Mona Ibrahim; Kalita, Golap; Kitazawa, Masashi; Tanemura, Masaki

    2017-01-01

    Low-temperature growth, as well as the transfer free growth on substrates, is the major concern of graphene research for its practical applications. Here we propose a simple method to achieve the transfer free graphene growth on SiO2 covered Si (SiO2/Si) substrate at 250 °C based on a solid-liquid-solid reaction. The key to this approach is the catalyst metal, which is not popular for graphene growth by chemical vapor deposition. A catalyst metal film of 500 nm thick was deposited onto an amorphous C (50 nm thick) coated SiO2/Si substrate. The sample was then annealed at 250 °C under vacuum condition. Raman spectra measured after the removal of the catalyst by chemical etching showed intense G and 2D peaks together with a small D and intense SiO2 related peaks, confirming the transfer free growth of multilayer graphene on SiO2/Si. The domain size of the graphene confirmed by optical microscope and atomic force microscope was about 5 μm in an average. Thus, this approach will open up a new route for transfer free graphene growth at low temperatures. PMID:28251997

  14. Graphene growth at the interface between Ni catalyst layer and SiO2/Si substrate.

    PubMed

    Lee, Jeong-Hoon; Song, Kwan-Woo; Park, Min-Ho; Kim, Hyung-Kyu; Yang, Cheol-Woong

    2011-07-01

    Graphene was synthesized deliberately at the interface between Ni film and SiO2/Si substrate as well as on top surface of Ni film using chemical vapor deposition (CVD) which is suitable for large-scale and low-cost synthesis of graphene. The carbon atom injected at the top surface of Ni film can penetrate and reach to the Ni/SiO2 interface for the formation of graphene. Once we have the graphene in between Ni film and SiO2/Si substrate, the substrate spontaneously provides insulating SiO2 layer and we may easily get graphene/SiO2/Si structure simply by discarding Ni film. This growth of graphene at the interface can exclude graphene transfer step for electronic application. Raman spectroscopy and optical microscopy show that graphene was successfully synthesized at the back of Ni film and the coverage of graphene varies with temperature and time of synthesis. The coverage of graphene at the interface depends on the amount of carbon atoms diffused into the back of Ni film.

  15. Alkaline-resistant titanium dioxide thin film displaying visible-light-induced superhydrophilicity initiated by interfacial electron transfer.

    PubMed

    Taguchi, Tsuyoshi; Ni, Lei; Irie, Hiroshi

    2013-04-16

    We synthesized a three-layer-type photocatalytic structure (TiO2/Cu(II)SiO2/SiO2), consisting of TiO2 on Cu(II)-grafted SiO2, which was deposited on a SiO2-coated glass substrate, and investigated its visible-light absorption and hydrophilic properties. Water contact angle measurements revealed visible-light-induced superhydrophilicity at the film surface that was initiated by interfacial electron transfer (IFET) at the interface of TiO2 and Cu(II)SiO2. Monitoring the oxidation state of Pb(2+) ions confirmed that the IFET-initiated holes diffused to the TiO2 surface, where they likely contributed to the hydrophilic conversion. We also demonstrated that layer-structured TiO2/Cu(II)SiO2/SiO2 was stable under alkaline conditions. Thus, we successfully synthesized alkaline-resistant TiO2 that displays visible-light-induced superhydrophilicity.

  16. Three-dimensional conductive networks based on stacked SiO2@graphene frameworks for enhanced gas sensing.

    PubMed

    Huang, Da; Yang, Zhi; Li, Xiaolin; Zhang, Liling; Hu, Jing; Su, Yanjie; Hu, Nantao; Yin, Guilin; He, Dannong; Zhang, Yafei

    2017-01-07

    Graphene is an ideal candidate for gas sensing due to its excellent conductivity and large specific surface areas. However, it usually suffers from sheet stacking, which seriously debilitates its sensing performance. Herein, we demonstrate a three-dimensional conductive network based on stacked SiO2@graphene core-shell hybrid frameworks for enhanced gas sensing. SiO2 spheres are uniformly encapsulated by graphene oxide (GO) through an electrostatic self-assembly approach to form SiO2@GO core-shell hybrid frameworks, which are reduced through thermal annealing to establish three-dimensional (3D) conductive sensing networks. The SiO2 supported 3D conductive graphene frameworks reveal superior sensing performance to bare reduced graphene oxide (RGO) films, which can be attributed to their less agglomeration and larger surface area. The response value of the 3D framework based sensor for 50 ppm NH3 and 50 ppm NO2 increased 8 times and 5 times, respectively. Additionally, the sensing performance degradation caused by the stacking of the sensing materials is significantly suppressed because the graphene layers are separated by the SiO2 spheres. The sensing performance decays by 92% for the bare RGO films when the concentration of the sensing material increases 8 times, while there is only a decay of 25% for that of the SiO2@graphene core-shell hybrid frameworks. This work provides an insight into 3D frameworks of hybrid materials for effectively improving gas sensing performance.

  17. Damage during SiO2 Etching by Low-Angle Forward Reflected Neutral Beam

    NASA Astrophysics Data System (ADS)

    Lee, Dohaing; Chung, Minjae; Park, Sangduk; Yeom, Geunyoung

    2002-12-01

    In this study, energetic reactive radical beams were formed with SF6 using a low-angle forward reflected neutral beam technique and the etch properties of SiO2 and possible damage induced by the radical beam were investigated. The results showed that when SiO2 was etched with the energetic reactive radical beams generated with SF6, SiO2 etch rates higher than 22 nm/min could be obtained. Also, when the etch damage was studied in terms of the capacitance-voltage (C-V) and current-voltage (I-V) characteristics of metal-nitride-oxide-silicon (MNOS) and metal-oxide-silicon (MOS) devices exposed to the radical beams, nearly no etch damage could be found.

  18. Direct observation of blocked nanoscale surface evaporation on SiO2 nanodroplets

    NASA Astrophysics Data System (ADS)

    Wan, Neng; Xu, Jun; Sun, Li-Tao; Martini, Matteo; Huang, Qing-An; Hu, Xiao-Hui; Xu, Tao; Bi, Heng-Chang; Sun, Jun

    2012-10-01

    Nano-scale surface evaporation of SiO2 nanodroplets from a volcano-shaped tip (tip diameter d ˜ 20 nm to 70 nm) was observed directly using an in situ transmission electron microscopy method. Au nanoparticles, those precipitated in the SiO2 matrix after an Au catalyzed growth, diffused and pinned onto the evaporation surface, which induced blocked evaporation dynamics. Our observations provide direct evidences of blocked evaporation dynamics caused by small-sized nanoparticles at the nanometer scale.

  19. Characterization and application of HfO2 - SiO2 mixtures produced by ion-beam sputtering technology

    NASA Astrophysics Data System (ADS)

    Kičas, S.; BatavičiÅ«tÄ--, GintarÄ--; Juškevičius, Kestutis; Tolenis, Tomas; Drazdys, Ramutis; Buzelis, Rytis; Melninkaitis, Andrius

    2013-11-01

    In the past years the usage of mixed oxides coatings lead to an important improvement of laser damage threshold and quality of optical elements. In this study influence of post treatment procedure - ex-situ annealing - is examined in terms of quality, optical constants and laser induced damage threshold (LIDT) of mixed HfO2 and SiO2 coatings. Monolayer thin films containing different fractions of HfO2 are deposited with ion beam sputtering technology (IBS.) All samples are post annealed at different temperatures and optimal regimes are defined. Refractive index and absorption coefficient dispersion is evaluated from transmission spectra measurements. Surface roughness of all samples is characterized before and after deposition and annealing, using atomic force microscopy (AFM). Microstructural changes are identified from changes in surface topography. Further, optical resistance was characterized by 5.7 ns duration pulses for 355 nm wavelength laser radiation, performing 1-on-1 sample exposure tests with high resolution micro-focusing approach for monolayer samples and S-on-1 tests for multilayer reflectors. Morphology of damaged sites was analyzed through optical microscopy. Finally, conclusions about annealing effect for mixed HfO2 and SiO2 monolayer and multilayer coatings are made.

  20. Structural, ferroelectric and optical properties of Bi2VO5.5 thin films deposited on platinized silicon {(100) Pt/TiO2/SiO2/Si} substrates

    NASA Astrophysics Data System (ADS)

    Kumari, N.; Krupanidhi, S. B.; Varma, K. B. R.

    2008-06-01

    Bismuth vanadate (Bi2VO5.5, BVO) thin films have been deposited by a pulsed laser ablation technique on platinized silicon substrates. The surface morphology of the BVO thin films has been studied by atomic force microscopy (AFM). The optical properties of the BVO thin films were investigated using spectroscopic ellipsometric measurements in the 300 820 nm wavelength range. The refractive index (n), extinction coefficient (k) and thickness of the BVO thin films have been obtained by fitting the ellipsometric experimental data in a four-phase model (air/BVOrough/BVO/Pt). The values of the optical constants n and k that were determined through multilayer analysis at 600 nm were 2.31 and 0.056, respectively. For fitting the ellipsometric data and to interpret the optical constants, the unknown dielectric function of the BVO films was constructed using a Lorentz model. The roughness of the films was modeled in the Brugmann effective medium approximation and the results were compared with the AFM observations.

  1. Structural and Electrical Characterization of SiO2 Gate Dielectrics Deposited from Solutions at Moderate Temperatures in Air.

    PubMed

    Esro, Mazran; Kolosov, Oleg; Jones, Peter J; Milne, William I; Adamopoulos, George

    2017-01-11

    Silicon dioxide (SiO2) is the most widely used dielectric for electronic applications. It is usually produced by thermal oxidation of silicon or by using a wide range of vacuum-based techniques. By default, the growth of SiO2 by thermal oxidation of silicon requires the use of Si substrates whereas the other deposition techniques either produce low quality or poor interface material and mostly require high deposition or annealing temperatures. Recent investigations therefore have focused on the development of alternative deposition paradigms based on solutions. Here, we report the deposition of SiO2 thin film dielectrics deposited by spray pyrolysis in air at moderate temperatures of ≈350 °C from pentane-2,4-dione solutions of SiCl4. SiO2 dielectrics were investigated by means of UV-vis absorption spectroscopy, spectroscopic ellipsometry, XPS, XRD, UFM/AFM, admittance spectroscopy, and field-effect measurements. Data analysis reveals smooth (RRMS < 1 nm) amorphous films with a dielectric constant of about 3.8, an optical band gap of ≈8.1 eV, leakage current densities in the order of ≈10(-7) A/cm(2) at 1 MV/cm, and high dielectric strength in excess of 5 MV/cm. XPS measurements confirm the SiO2 stoichiometry and FTIR spectra reveal features related to SiO2 only. Thin film transistors implementing spray-coated SiO2 gate dielectrics and C60 and pentacene semiconducting channels exhibit excellent transport characteristics, i.e., negligible hysteresis, low leakage currents, high on/off current modulation ratio on the order of 10(6), and high carrier mobility.

  2. Dielectric SiO2 Planarization Using MnO2 Slurry

    NASA Astrophysics Data System (ADS)

    Kishii, Sadahiro; Nakamura, Ko; Hanawa, Kenzo; Watanabe, Satoru; Arimoto, Yoshihiro; Kurokawa, Syuhei; Doi, Toshiro K.

    2012-01-01

    MnO2 slurry can polish SiO2 film faster and planarize wide feature steps (2 ×2 mm2) to a lower height than conventional silica slurry. A comparison of Gibbs free energies indicates that the MnO2 abrasive directly reacts on the SiO2 film. In post-Chemical mechanical polishing (CMP), the MnO2 abrasive can be completely removed by dipping it in mixed solutions of inorganic acids and H2O2 followed by scrubbing and dipping in HF solution. A comparison of Gibbs free energies clarifies that the MnO2 abrasive on the wafer is easily dissolved in a mixed solution of an inorganic acid and H2O2.

  3. Synthesis and characterization of amorphous SiO2 nanowires via pulsed laser deposition accompanied by N2 annealing

    NASA Astrophysics Data System (ADS)

    Li, Hui; Guan, Leilei; Xu, Zhuoqi; Zhao, Yu; Sun, Jian; Wu, Jiada; Xu, Ning

    2016-12-01

    Amorphous SiO2 nanowires are successfully fabricated on fused silica substrates covered by nickel/carbon catalyst bilayers via a method of pulsed laser deposition accompanied by annealing in ambient N2. The field emission scanning electron microscopy images show that the optimum annealing temperature for the growth of SiO2 nanowires is about 1200 °C and the grown SiO2 nanowires become denser, longer and more uniform with the increment of annealing duration. The results of transmission electron microscopy and high-resolution transmission electron microscopy show that the grown nanowires are amorphous and have dark spheres on their tops. The analyses of energy dispersive X-ray spectroscopy reveal that the nanowires are composed of SiO2 and the dark spheres on their tops contain little nickel. It is inferred that nickel, carbon and CO are the key elements to promote the SiO2 nanowire growth in the solid-liquid-solid mode. Transmission spectra demonstrate that the as-grown nanowire thin films can have about 94% average transmittance in the range of 350-800 nm, meanwhile the photoluminescence spectra of the as-grown SiO2 nanowire samples show stable ultraviolet emission centered at about 363 nm with a shoulder at about 393 nm.

  4. Y1Ba2Cu3O(6+delta) growth on thin Y-enhanced SiO2 buffer layers on silicon

    NASA Technical Reports Server (NTRS)

    Robin, T.; Mesarwi, A.; Wu, N. J.; Fan, W. C.; Espoir, L.; Ignatiev, A.; Sega, R.

    1991-01-01

    SiO2 buffer layers as thin as 2 nm have been developed for use in the growth of Y1Ba2Cu3O(6+delta) thin films on silicon substrates. The SiO2 layers are formed through Y enhancement of silicon oxidation, and are highly stoichiometric. Y1Ba2Cu3O(6+delta) film growth on silicon with thin buffer layers has shown c orientation and Tc0 = 78 K.

  5. TiO2/SiO2 porous composite thin films: Role of TiO2 areal loading and modification with gold nanospheres on the photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Levchuk, Irina; Sillanpää, Mika; Guillard, Chantal; Gregori, Damia; Chateau, Denis; Parola, Stephane

    2016-10-01

    The aim of the work was to study photocatalytic activity of composite TiO2/Au/SiO2 thin films. Coatings were prepared using sol-gel technique. Physicochemical parameters of coatings were characterized using UV-vis spectrometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectrometry (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES), ellipsometry, tactile measurements, goniometry and diffuse reflectance measurements. The photocatalytic activity of the films was tested in batch mode using aqueous solution of formic acid. Changes of formic acid concentration were determined by means of high pressure liquid chromatography (HPLC). Increase of initial degradation rate of formic acid was detected for TiO2/Au/SiO2 films with gold nanoparticle's load 0.5 wt.% and 1.25 wt.%. However, deeper insights using more detailed characterization of these coatings demonstrated that the improvement of the photocatalytic activity is more probably attributed to an increase in the areal loading of TiO2.

  6. Screen-printed photochromic textiles through new inks based on SiO2@naphthopyran nanoparticles.

    PubMed

    Pinto, Tânia V; Costa, Paula; Sousa, Céu M; Sousa, Carlos A D; Pereira, Clara; Silva, Carla J S M; Pereira, Manuel Fernando R; Coelho, Paulo J; Freire, Cristina

    2016-10-05

    Photochromic silica nanoparticles (SiO2@NPT), fabricated through covalent immobilization of silylated naphthopyrans based on 2H-naphtho[1,2-b]pyran (S1, S2) and 3H-naphtho[2,1-b]pyran (S3, S4) or through direct adsorption of parent naphthopyrans (NPT 1, 3) onto silica nanoparticles, were successfully incorporated onto cotton fabrics by screen-printing process. Two aqueous acrylic (AC) and polyurethane (PU)-based inks were used as dispersing media. All textiles exhibited reversible photochromism under UV and solar irradiation, developing fast response and intense coloration. The fabrics coated with SiO2@S1 and SiO2@S2 showed a rapid color change and high contrast (ΔE*ab = 39-52), despite presenting slower bleaching kinetics (2-3 h to fade to the original color), whereas the textiles coated with SiO2@S3 and SiO2@S4 exhibited an excellent engagement between coloration and decoloration rates (coloration and fading times of 1 and 2 min, respectively; ΔE*ab = 27-53). The PU-based fabrics showed excellent results during the washing fastness tests, while the AC-based textiles only evidenced good results when a protective transfer film was applied over the printed design. In general, all textiles presented high color contrast, high photostability (during continuous UV irradiation) and stable photochromic responses upon twelve successive UV light/dark cycles, becoming excellent alternatives to other photochromic textiles reported in the literature.

  7. Evidence of swelling of SiO2 upon thermal annealing

    NASA Astrophysics Data System (ADS)

    Banerjee, S.; Chakraborty, S.; Lai, P. T.

    2002-04-01

    Ultrathin SiO2 film was thermally grown on Si(001) substrate by dry oxidation and wet oxidation processes. The films were then subjected to thermal annealing (TA) at 1000 °C for 30 min. The structural characterization of the as-grown and the TA samples was carried out using the grazing incidence x-ray reflectivity technique. The analysis of the x-ray reflectivity data was carried out by using a model independent formalism based on the distorted wave Born approximation for obtaining the electron density profile (EDP) of the film as a function of depth. The EDP of both films show a decrease in the electron density as well as an increase in their thickness when the films are subjected to TA. It has also been observed that the total number of electrons is conserved in the oxide film after TA. Our analysis of the x-ray reflectivity data indicates that the SiO2 film swells and its interface with the substrate modifies upon TA.

  8. REE-SIO2 Systematics in Mor Gabbros and Associated Plagiogranites from the Fournier Oceanic Fragment, New Brunswick, Canada

    NASA Astrophysics Data System (ADS)

    Brophy, J. G.

    2010-12-01

    Seawater influx into hot, dry MOR gabbro can initiate hydration-induced melting and the generation of intermediate to felsic partial melts collectively referred to as plagiogranite. In a recent modeling study, Brophy (2009) suggested that the REE abundances of partial melts generated in this fashion should be characterized by unique patterns of REE-SiO2 variation. Specifically, REE abundances (modeled as enrichment factors, Cl/Co) should show a positive correlation with increasing SiO2 up to around 60 wt. % followed by a steady decrease in abundance as liquid SiO2 increases to around 76%. For liquids of around 55% SiO2 the degree of enrichment is around 2 for all of the REE. However, Cl/Co in the intermediate liquids of around 60 % SiO2 steadily decreases from ~5 for La to ~3 for Yb. Simarlarly, Cl/Co in the high SiO2 liquids of around 76% SiO2 decrease from ~3 for La to ~1 for Yb. If these model predictions are correct, the REE-SiO2 systematics of any naturally occurring suite of plagiogranite and MOR gabbro could be used to assess a partial melting as opposed to crystal fractionation origin. To test the model predictions, a suite of MOR gabbros and intrusive veins of plagiogranite were collected from the Fournier Oceanic Fragment, a middle Ordovician ophiolite sequence located along the northern shore of New Brunswick, and the type exposure for plagiogranites generated by hydration-induced MOR gabbro melting (Flagler and Spray, 1991). The MOR gabbros range from 48 to 55 % SiO2 while the intrusive plagiogranites range from 57 to 78 % SiO2 (anhydrous basis). When REE abundances are plotted against whole rock SiO2 they show all of the model features described above, though the absolute abundances require an initial gabbroic source rock that is more enriched in the REE than the host gabbros themselves. This correspondence between modeled and observed REE- SiO2 variations confirms the model predictions of Brophy (2009) and suggests that REE- SiO2 systematics represent

  9. Fabrication of high performance thin-film transistors via pressure-induced nucleation.

    PubMed

    Kang, Myung-Koo; Kim, Si Joon; Kim, Hyun Jae

    2014-10-31

    We report a method to improve the performance of polycrystalline Si (poly-Si) thin-film transistors (TFTs) via pressure-induced nucleation (PIN). During the PIN process, spatial variation in the local solidification temperature occurs because of a non-uniform pressure distribution during laser irradiation of the amorphous Si layer, which is capped with an SiO2 layer. This leads to a four-fold increase in the grain size of the poly-Si thin-films formed using the PIN process, compared with those formed using conventional excimer laser annealing. We find that thin films with optimal electrical properties can be achieved with a reduction in the number of laser irradiations from 20 to 6, as well as the preservation of the interface between the poly-Si and the SiO2 gate insulator. This interface preservation becomes possible to remove the cleaning process prior to gate insulator deposition, and we report devices with a field-effect mobility greater than 160 cm(2)/Vs.

  10. Properties of SiO2 grown on Ti, Co, Ni, Pd, and Pt silicides

    NASA Astrophysics Data System (ADS)

    Bartur, M.; Nicolet, M.-A.

    1984-01-01

    Successful utilization of silicides for VLSI applcations depends strongly on the formation of electrically insulating oxide on top of the silicide (1) . It is found that almost all silicides on a Si substrate can be oxidized to form an SiO2 layer on their surface. In this paper, we present some of the properties of such SiO2 layers formed on TiSi2, CoSi2, NiSi2, Pd2Si, and PtSi on a substrate following dry and wet oxidation. Electrical parameters that were investigated are the dielectric constant, dielectric strength (breakdown field), and pinhole density. The dielectric constant was found to be 3.49 ± 0.24, which is similar to the values reported for SiO2 grown on Si. The dielectric strength of the oxide layers depends on the polarity of the applied voltage, as is the case for oxide grown on poly-Si. Pinhole density in this oxide was also estimated and is less than 40 per cm2. The oxide density and stoichiometry were evaluated using Rutherford Backscattering Spectrometry (RBS) and DEKTAK, and compared to SiO2 grown on . The conclusion we have reached is that oxides grown on almost all the silicides investigated (except PdSi), hold promise for integrated circuit application. The main problem is the suicide roughness, induced by the thermal oxidation, that reduces the dielectric breakdown field.

  11. Growth of SiO 2 on InP substrate by liquid phase deposition

    NASA Astrophysics Data System (ADS)

    Lei, Po Hsun; Yang, Chyi Da

    2010-04-01

    We have grown silicon dioxide (SiO 2) on indium phosphorous (InP) substrate by liquid phase deposition (LPD) method. With inserting InP wafer in the treatment solution composed of SiO 2 saturated hydrofluorosilicic acid (H 2SiF 6), 0.1 M boric acid (H 3BO 3) and 1.74 M diluted hydrochloric acid (HCl), the maximum deposition rate and refractive index for the as-grown LPD-SiO 2 film were about 187.5 Å/h and 1.495 under the constant growth temperature of 40 °C. The secondary ion mass spectroscope (SIMS) and energy dispersive X-ray (EDX) confirmed that the elements of silicon, oxygen, and chloride were found in the as-grown LPD-SiO 2 film. On the other hand, the effects of treatment solution incorporated with the hydrogen peroxide (H 2O 2) that can regulate the concentration of OH - ion were also shown in this article. The experimental results represented that the deposition rate decreases with increasing the concentration of hydrogen peroxide due to the reduced concentration of SiO 2 saturated H 2SiF 6 in treatment solution.

  12. Study of the kinetics and mechanism of the thermal nitridation of SiO2

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Madhukar, A.; Grunthaner, F. J.; Naiman, M. L.

    1985-01-01

    X-ray photoelectron spectroscopy (XPS) has been used to study the nitridation time and temperature dependence of the nitrogen distribution in thermally nitrided SiO2 films. The XPS data show that the maximum nitrogen concentration near the (SiO(x)N(y)/Si interface is initially at the interface, but moves 20-25 A away from the interface with increasing nitridation time. Computer modeling of the kinetic processes involved is carried out and reveals a mechanism in which diffusing species, initially consisting primarily of nitrogen, react with the substrate, followed by formation of the oxygen-rich oxynitride due to reaction of the diffusing oxygen displaced by the slower nitridation of the SiO2. The data are consistent with this mechanism provided the influence of the interfacial strain on the nitridation and oxidation kinetics is explicitly accounted for.

  13. Synthesis and size differentiation of Ge nanocrystals in amorphous SiO2

    NASA Astrophysics Data System (ADS)

    Ağan, S.; Çelik-Aktaş, A.; Zuo, J. M.; Dana, A.; Aydınlı, A.

    2006-04-01

    Germanosilicate layers were grown on Si substrates by plasma enhanced chemical vapor deposition (PECVD) and annealed at different temperatures ranging from 700 1010 °C for durations of 5 to 60 min. Transmission electron microscopy (TEM) was used to investigate Ge nanocrystal formation in SiO2:Ge films. High-resolution cross section TEM images, electron energy-loss spectroscopy and energy dispersive X-ray analysis (EDX) data indicate that Ge nanocrystals are present in the amorphous silicon dioxide films. These nanocrystals are formed in two spatially separated layers with average sizes of 15 and 50 nm, respectively. EDX analysis indicates that Ge also diffuses into the Si substrate.

  14. Formation and microstructural properties of locally distributed ZnSiO3 nanoparticles embedded in a SiO2 layer by using a focused electron beam.

    PubMed

    Shin, J W; No, Y S; Kim, T W; Choi, W K

    2008-10-01

    Locally distributed crystalline ZnSiO3 nanoparticles embedded in a SiO2 layer inserted between the ZnO thin film and the Si substrate were formed using transmission electron microscopy (TEM) with a focused electron beam irradiation process. High-resolution TEM (HRTEM) images and energy dispersive X-ray spectroscopy (EDS) profiles showed that ZnSiO3 nanocrystals with a size of approximately 6 nm were formed in the SiO2 layer. The formation mechanisms of the ZnSiO3 nanocrystals in the SiO2 layer are described on the basis of the HRTEM images and the EDS profiles.

  15. 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

  16. A kinetic model for the thermal nitridation of SiO2/Si

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Madhukar, A.

    1986-01-01

    To explain the observed nitrogen distributions in thermally nitridated SiO2 films, a kinetic model is proposed in which the nitridation process is simulated, using the first-order chemical kinetics and Arrhenius dependence of the diffusion and reaction rates on temperature. The calculations show that initially, as the substrate reacts with diffusing nitrogen, a nitrogen-rich oxynitride forms at the SiO2-Si interface, while at nitridation temperatures above 1000 C, an oxygen-rich oxynitride subsequently forms at the interface, due to reaction of the substrate with an increasingly concentrated oxygen displaced by the slower nitridation of the SiO2. This sequence of events results in a nitrogen distribution in which the peak of the interfacial nitrogen concentration occurs away from the interface. The results are compared with the observed nitrogen distribution. The calculated results have correctly predicted the positions of the interfacial nitrogen peaks at the temperatures of 800, 1000, and 1150 C. To account for the observed width of the interfacial nitrogen distribution, it was found necessary to include in the simulations the effect of interfacial strain.

  17. Highly transparent and efficient counter electrode using SiO2/PEDOT-PSS composite for bifacial dye-sensitized solar cells.

    PubMed

    Song, Dandan; Li, Meicheng; Li, Yingfeng; Zhao, Xing; Jiang, Bing; Jiang, Yongjian

    2014-05-28

    A highly transparent and efficient counter electrode was facilely fabricated using SiO2/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) inorganic/organic composite and used in bifacial dye-sensitized solar cells (DSCs). The optical properties of SiO2/PEDOT-PSS electrode can be tailored by the blending amount of SiO2 and film thickness, and the incorporation of SiO2 in PEDOT-PSS provides better transmission in the long wavelength range. Meanwhile, the SiO2/PEDOT-PSS counter electrode shows a better electrochemical catalytic activity than PEDOT-PSS electrode for triiodide reduction, and the role of SiO2 in the catalytic process is investigated. The bifacial DSC with SiO2/PEDOT-PSS counter electrode achieves a high power conversion efficiency (PCE) of 4.61% under rear-side irradiation, which is about 83% of that obtained under front-side irradiation. Furthermore, the PCE of bifacial DSC can be significantly increased by adding a reflector to achieve bifacial irradiation, which is 39% higher than that under conventional front-side irradiation.

  18. Effects of thermal annealing on the structural and optical properties of carbon-implanted SiO2.

    PubMed

    Poudel, P R; Paramo, J A; Poudel, P P; Diercks, D R; Strzhemechny, Y M; Rout, B; McDaniel, F D

    2012-03-01

    Amorphous carbon (a-C) nanoclusters were synthesized by the implantation of carbon ions (C-) into thermally grown silicon dioxide film (-500 nm thick) on a Si (100) wafer and processed by high temperature thermal annealing. The carbon ions were implanted with an energy of 70 keV at a fluence of 5 x 10(17) atoms/cm2. The implanted samples were annealed at 1100 degrees C for different time periods in a gas mixture of 96% Ar+4% H2. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and High Resolution Transmission Electron Microscopy (HRTEM) were used to study the structural properties of both the as-implanted and annealed samples. HRTEM reveals the formation of nanostructures in the annealed samples. The Raman spectroscopy also confirms the formation of carbon nano-clusters in the samples annealed for 10 min, 30 min, 60 min and 90 min. No Raman features originating from the carbon-clusters are observed for the sample annealed further to 120 min, indicating a complete loss of implanted carbon from the SiO2 layer. The loss of the implanted carbon in the 120 min annealed sample from the SiO2 layer was also observed in the XPS depth profile measurements. Room temperature photoluminescence (PL) spectroscopy revealed visible emissions from the samples pointing to carbon ion induced defects as the origin of a broad 2.0-2.4 eV band, and the intrinsic defects in SiO2 as the possible origin of the -2.9 eV bands. In low temperature photoluminescence spectra, two sharp and intense photoluminescence lines at -3.31 eV and -3.34 eV appear for the samples annealed for 90 min and 120 min, whereas no such bands are observed in the samples annealed for 10 min, 30 min, and 60 min. The Si nano-clusters forming at the Si-SiO2 interface could be the origin of these intense peaks.

  19. Analysis of SiO 2/TiO 2-SiO 2/SiO 2 coupled parallel waveguide structures using computer aided design techniques

    NASA Astrophysics Data System (ADS)

    Chaudhari, Chitrarekha; Gautam, D. K.

    2000-07-01

    The analysis of two coupled parallel rib waveguides of SiO 2/TiO 2-SiO 2/SiO 2 on silicon substrate is presented. The indigenously developed beam propagation method (BPM) simulation tools are applied to observe the power coupling between two identical parallel rib waveguides and to study the dependence of the coupling length on various parameters of the rib waveguides including the refractive indices, rib height, guide thickness, clad thickness and separation between them. The designs for the 3 dB coupler and demultiplexer for DWDM, based on the symmetric directional coupler, are optimized for minimum dimensions using the techniques, for the first time. The optimum device length for 3 dB coupler was calculated to be 650 μm with 0.016 dB losses. The 1.3 μm and 1.304 μm demultiplexer has been designed with the optimized device length of 1.02 mm and the losses less than 0.40 dB at both the wavelengths.

  20. Devitrification and delayed crazing of SiO2 on single-crystal silicon and chemically vapor-deposited silicon nitride

    NASA Technical Reports Server (NTRS)

    Choi, Doo Jin; Scott, William D.

    1987-01-01

    The linear growth rate of cristobalite was measured in thin SiO2 films on silicon and chemically vapor-deposited silicon nitride. The presence of trace impurities from alumina furnace tubes greatly increased the crystal growth rate. Under clean conditions, the growth rate was still 1 order-of-magnitude greater than that for internally nucleated crystals in bulk silica. Crystallized films cracked and lifted from the surface after exposure to atmospheric water vapor. The crystallization and subsequent crazing and lifting of protective SiO2 films on silicon nitride should be considered in long-term applications.

  1. Intensity analysis of XPS spectra to determine oxide uniformity - Application to SiO2/Si interfaces

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Grunthaner, F. J.

    1980-01-01

    A simple method of determining oxide uniformity is derived which requires no knowlege of film thickness, escape depth, or film composition. The method involves only the measurement of oxide and substrate intensities and is illustrated by analysis of XPS spectral data for thin SiO2 films grown both thermally and by low-temperature chemical vapor deposition on monocrystalline Si. A region 20-30 A thick is found near the SiO2/Si interface on thermally oxidized samples which has an inelastic mean free path 35% less than that found in the bulk oxide. This is interpreted as being due to lattice mismatch resulting in a strained region which is structurally, but not stoichiometrically, distinct from the bulk oxide.

  2. Scalable flame synthesis of SiO2 nanowires: dynamics of growth.

    PubMed

    Tricoli, Antonio; Righettoni, Marco; Krumeich, Frank; Stark, Wendelin J; Pratsinis, Sotiris E

    2010-11-19

    Silica nanowire arrays were grown directly onto plain glass substrates by scalable flame spray pyrolysis of organometallic solutions (hexamethyldisiloxane or tetraethyl orthosilicate). The silicon dioxide films consisted of a network of interwoven nanowires from a few to several hundred nanometres long (depending on the process conditions) and about 20 nm in diameter, as determined by scanning electron microscopy. These films were formed rapidly (within 10-20 s) at high growth rates (ca 11-30 nm s(-1)) by chemical vapour deposition (surface growth) at ambient conditions on the glass substrate as determined by thermophoretic sampling of the flame aerosol and microscopy. In contrast, on high purity quartz nearly no nanowires were grown while on steel substrates porous SiO(2) films were formed. Functionalization with perfluorooctyl triethoxysilane converted the nanowire surface from super-hydrophilic to hydrophobic. Additionally, their hermetic coating by thin carbon layers was demonstrated also revealing their potential as substrates for synthesis of other functional 1D composite structures. This approach is a significant step towards large scale synthesis of SiO(2) nanowires facilitating their utilization in several applications.

  3. Scalable flame synthesis of SiO2 nanowires: dynamics of growth

    PubMed Central

    Tricoli, Antonio; Righettoni, Marco; Krumeich, Frank; Stark, Wendelin J; Pratsinis, Sotiris E

    2013-01-01

    Silica nanowire arrays were grown directly onto plain glass substrates by scalable flame spray pyrolysis of organometallic solutions (hexamethyldisiloxane or tetraethyl orthosilicate). The silicon dioxide films consisted of a network of interwoven nanowires from a few to several hundred nanometres long (depending on the process conditions) and about 20 nm in diameter, as determined by scanning electron microscopy. These films were formed rapidly (within 10–20 s) at high growth rates (ca 11–30 nm s−1) by chemical vapour deposition (surface growth) at ambient conditions on the glass substrate as determined by thermophoretic sampling of the flame aerosol and microscopy. In contrast, on high purity quartz nearly no nanowires were grown while on steel substrates porous SiO2 films were formed. Functionalization with perfluorooctyl triethoxysilane converted the nanowire surface from super-hydrophilic to hydrophobic. Additionally, their hermetic coating by thin carbon layers was demonstrated also revealing their potential as substrates for synthesis of other functional 1D composite structures. This approach is a significant step towards large scale synthesis of SiO2 nanowires facilitating their utilization in several applications. PMID:20972311

  4. Lithiation of SiO2 in Li-ion batteries: in situ transmission electron microscopy experiments and theoretical studies.

    PubMed

    Zhang, Yuefei; Li, Yujie; Wang, Zhenyu; Zhao, Kejie

    2014-12-10

    Surface passivation has become a routine strategy of design to mitigate the chemomechanical degradation of high-capacity electrodes by regulating the electrochemical process of lithiation and managing the associated deformation dynamics. Oxides are the prevalent materials used for surface coating. Lithiation of SiO2 leads to drastic changes in its electro-chemo-mechanical properties from an electronic insulator and a brittle material in its pure form to a conductor and a material sustainable of large deformation in the lithiated form. We synthesized SiO2-coated SiC nanowires that allow us to focus on the lithiation behavior of the sub-10 nm SiO2 thin coating. We systematically investigate the structural evolution, the electronic conduction and ionic transport properties, and the deformation pattern of lithiated SiO2 through coordinated in situ transmission electron microcopy experiments, first-principles computation, and continuum theories. We observe the stress-mediated reaction that induces inhomogeneous growth of SiO2. The results provide fundamental perspectives on the chemomechanical behaviors of oxides used in the surface coating of Li-ion technologies.

  5. Local atomic and electronic structure of oxide/GaAs and SiO2/Si interfaces using high-resolution XPS

    NASA Technical Reports Server (NTRS)

    Grunthaner, F. J.; Grunthaner, P. J.; Vasquez, R. P.; Lewis, B. F.; Maserjian, J.; Madhukar, A.

    1979-01-01

    The chemical structures of thin SiO2 films, thin native oxides of GaAs (20-30 A), and the respective oxide-semiconductor interfaces, have been investigated using high-resolution X-ray photoelectron spectroscopy. Depth profiles of these structures have been obtained using argon ion bombardment and wet chemical etching techniques. The chemical destruction induced by the ion profiling method is shown by direct comparison of these methods for identical samples. Fourier transform data-reduction methods based on linear prediction with maximum entropy constraints are used to analyze the discrete structure in oxides and substrates. This discrete structure is interpreted by means of a structure-induced charge-transfer model.

  6. Dissolution Kinetics of SiO2 into CaO-Fe2O3-SiO2 Slag

    NASA Astrophysics Data System (ADS)

    Yu, Bin; Lv, Xuewei; Xiang, Shenglin; Xu, Jian

    2016-06-01

    High-basicity sinter is the predominant Fe-bearing material used in blast furnace process in East Asia. The dissolution of SiO2 into molten calcium ferrite influences the assimilation process. In this study, a rotating cylinder method was used to explore the dissolution kinetics of SiO2 into CaO-Fe2O3-SiO2 slag. The influencing factors, including temperature, rotating time and speed, and initial composition of the slag, were considered. Results showed that the dissolution rate increased with increasing rotation speed and temperature, whereas the increase in ω(SiO2) or ω(Fe2O3)/ ω(CaO) ratio in the initial slag composition decreased the dissolution rate. The diffusion coefficient and activation energy of SiO2 during the dissolution process ranged from 2.09 × 10-6 to 6.40 × 10-6 cm2 s-1 and 106.62 to 248.20 kJ mol-1, respectively. Concentration difference between the boundary layer and bulk phase was the primary driving force of the dissolution process; however, this process was also influenced by the slag viscosity and ion diffusivity.

  7. Coulomb-blockade peak spacing statistics of graphene quantum dots on SiO2

    NASA Astrophysics Data System (ADS)

    Herrmann, O.; Gould, C.; Molenkamp, L. W.

    2016-10-01

    Extrinsic disorder strongly affects the performance of graphene-based quantum dots. The standard SiO2 substrate is generally considered to be one major factor besides edge-induced disorder. In this report we present the fabrication of lithographically defined quantum dots on SiO2 with short and narrow constrictions and different central island sizes. Low temperature transport measurements display distinct Coulomb-blockade peaks with amplitudes exceeding what is commonly observed experimentally. The analysis of the normalized Coulomb-blockade peak spacing shows a size dependence, which has not previously been observed for devices on SiO2. Furthermore, a quantitative comparison of the peak spacing distribution to the literature shows that one of the two devices compares favorably to a similar sized dot placed on hexagonal boron nitride, which is known to reduce the substrate disorder. Our findings suggest that the other sources of extrinsic disorder, such as lithography residues, may play an important role for the performance of large graphene quantum dots.

  8. Multilayers of oppositely charged SiO2 nanoparticles: effect of surface charge on multilayer assembly.

    PubMed

    Lee, Daeyeon; Gemici, Zekeriyya; Rubner, Michael F; Cohen, Robert E

    2007-08-14

    The growth behavior of all-silica nanoparticle multilayer thin films assembled via layer-by-layer deposition of oppositely charged SiO2 nanoparticles was studied as a function of assembly conditions. Amine-functionalized SiO2 nanoparticles were assembled into multilayers through the use of three different sizes of negatively charged SiO2 nanoparticles. The assembly pH of the nanoparticle suspensions needed to achieve maximum growth for each system was found to be different. However, the surface charge /z/ of the negatively charged silica nanoparticles at the optimal assembly pH was approximately the same, indicating the importance of this parameter in determining the growth behavior of all-nanoparticle multilayers. When /z/ of the negatively charged nanoparticles lies between 0.6z(0) and 1.2z(0) (where z(0) is the pH-independent value of the zeta-potential of the positively charged nanoparticles used in this study), the multilayers show maximum growth for each system. The effect of particle size on the film structure was also investigated. Although nanoparticle size significantly influenced the average bilayer thickness of the multilayers, the porosity and refractive index of multilayers made from nanoparticles of different sizes varied by a small amount. For example, the porosity of the different multilayer systems ranged from 42 to 49%. This study further demonstrates that one-component all-nanoparticle multilayers can be assembled successfully by depositing nanoparticles of the same material but with opposite surface charge.

  9. Synchrotron x-ray studies of vitreous SiO2 over Si(001). I. Anisotropic glass contribution

    NASA Astrophysics Data System (ADS)

    Castro-Colin, M.; Donner, W.; Moss, S. C.; Islam, Z.; Sinha, S. K.; Nemanich, R.; Metzger, H. T.; Bösecke, P.; Shülli, T.

    2005-01-01

    While numerous investigations of the structure and interface of amorphous SiO2 thermally grown on Si, theoretical as well as experimental, have been carried out over the years, a definitive picture of this thin gate oxide and its interface remains lacking. We have explored this issue using synchrotron x rays in grazing incidence geometry. In this geometry a fourfold modulation in the first sharp diffraction peak (FSDP) from thin vitreous SiO2 of 100 and 500 Å thickness can be observed. While the FSDP exhibits a modulation throughout the entire film, this modulation decays away from the interface. Reflectivity measurements were also performed, which reveal an interfacial layer of 3% density increase in the SiO2 film over the bulk (film) density.

  10. Migration of organic residuals in interlayer oxide to {SiO2}/{Si} interface

    NASA Astrophysics Data System (ADS)

    Kodama, N.; Mori, H.; Saito, S.; Koyama, K.

    1996-09-01

    The isolation characteristics of COB (capacitor over bit-line)-DRAMs was degraded, only when TEOS (tetraethyl orthosilicate)-BPSG (boron phosphor silicate glass) film was used for the interlayer oxide, which was covered with the silicon nitride film. The measurement of Vfb (flat band voltage) of the capacitor indicated that there were the positive charges around the {SiO2}/{Si} interface, which made the substrate n-type. SIMS (Secondary Ion Mass Spectrometry) by detecting MCs + ions showed that the amount of piled-up carbon at the interface increased with increasing annealing temperature, and this increase was consistent with the Vfb shift. Therefore, the isolation degradation was considered to be caused by positive charges which were originated from piled-up carbon. The SIMS analysis also showed that the total amount of carbon in the oxide seemed to be unchanged by the heat treatment, indicating that residual organic compounds migrated from the TEOS-BPSG layer to the {SiO2}/{Si} interface during the heat treatment, since the silicon nitride layer prevented their out-diffusion.

  11. Enhanced photoluminescence from CdS with SiO2 nanopillar arrays

    PubMed Central

    Li, Wei; Wang, Shaolei; He, Sufeng; Wang, Jing; Guo, Yanyan; Guo, Yufeng

    2015-01-01

    In this paper, the enhanced photoluminescence from CdS thin film with SiO2 nanopillar array (NPA) was demonstrated. The CdS was prepared using chemical bath deposition in a solution bath containing CdSO4, SC(NH2)2, and NH4OH. The SiO2 NPA was fabricated by the nanosphere lithography (NSL) techniques. The nanopillar is about 50 nm in diameter, and the height is 150 nm. As a result, the sample with NPA shows an obvious improvement of photoluminescence (PL), compared with the one without NPA. In addition, we also observed that the PL intensity is increased ~5 times if the active layer is deposited on the nanopillar arrays and covered by a thin metal film of Al. It is noteworthy that the enhancement of photoluminescence could be attributed to the roughness of the surface, the 2D photonic band gap (PBG) effect and the surface plasmon resonance (SPR) effects. PMID:26077552

  12. Diffusion of SiO2 in Rhyolitic Melt

    NASA Astrophysics Data System (ADS)

    Yu, Y.; Zhang, Y.; Yang, Y.

    2015-12-01

    SiO2 is the most major component in silicate melts, and the diffusion of SiO2 plays a controlling role in growth or dissolution of quartz from or into silicate melts. The diffusivity of SiO2 is small and highly dependent on melt compositions (Lesher and Walker, 1986; Koyaguchi, 1989), making it difficult to extract high-quality Si diffusivity data. We conducted quartz dissolution experiments in rhyolitic melt (0.1wt% H2O, 73 wt% SiO2) at 1300-1600 °C. We also have preliminary data on quartz dissolution in basaltic melt at 1300 °C , one quartz dissolution experiment (Zhang et al., 1989) in andesitic melt at 1300 °C , and five cassiterite dissolution experiments (Yang et al, in review) in various hydrous rhyolitic melts (containing 0.1-5.9 wt% H2O, and 74-77 wt% SiO2) at 900-1100 °C. All experiments were conducted at 0.5 GPa using piston cylinder apparatus. All data were combined to examine the dependence of DSiO2 on melt compositions. Though in individual experiments lnDSiO2 is a linear function of SiO2 concentration as shown in literature, the combined data show that lnDSiO2 decreases linearly with XSi+Al, where XSi+Al is defined as cation mole fraction of Si+Al in melts. By fitting concentration profiles at different temperatures using DSiO2 = D0 ea(1-XSi+Al), the results show that the parameter a is roughly composition-independent across all experiments and is linear to 1/T: a = 2.603(±0.451) + 35282(±627)/T, r2= 0.996. D0 is the extrapolated effective binary diffusivity of SiO2 in pure silica melt (XSi+Al = 1 roughly corresponds to XSi = 1 in quartz dissolution experiments). For quartz dissolution experiments in rhyolitic melt, the dependence of D0 on T is: lnD0 = -14.041(±1.915) - 34719(±3125)/T, r2= 0.875 For cassiterite dissolution, lnD0 values do not follow the above trend because the dominant SnO concentration gradient can affect interdiffusion between SiO2 and other components. That is, XSi+Al alone is not enough to account for how D0 depends on other components. The effect of H2O on both a and D0 is roughly accounted for by simply including H as a cation when calculating XSi+Al. Namely, adding H2O equals to lowering XSi+Al, e.g. at 1300°C, every addition of 1 wt% H2O (i.e. lowering XSi+Al by ~0.05) would increase DSiO2 by ~1.2 lnD units for a melt with initial XSi+Al = 0.85 on anhydrous basis.

  13. Extracting the Density of States of Copper Phthalocyanine at the SiO2 Interface with Electronic Sum Frequency Generation.

    PubMed

    Pandey, Ravindra; Moon, Aaron P; Bender, Jon A; Roberts, Sean T

    2016-03-17

    Organic semiconductors (OSCs) constitute an attractive platform for optoelectronics design due to the ease of their processability and chemically tunable properties. Incorporating OSCs into electrical circuits requires forming junctions between them and other materials, yet the change in dielectric properties about these junctions can strongly perturb the electronic structure of the OSC. Here we adapt an interface-selective optical technique, electronic sum frequency generation (ESFG), to the study of a model OSC thin-film system, copper phthalocyanine (CuPc) deposited on SiO2. We find that by modeling the thickness dependence of our measured spectra, we can identify changes in CuPc's electronic density of states at both its buried interface with SiO2 and air-exposed surface. Our work demonstrates that ESFG can be used to noninvasively probe the interfacial electronic structure of optically thick OSC films, indicating that it can be used for the study of OSC-based optoelectronics in situ.

  14. Surface Modification in Control SiO2 Fiber Fracture.

    DTIC Science & Technology

    1981-10-01

    assuming the Lennard - Jones potential . The results show that the potential due to the dispersion forces falls obB if rapidly with the distance from...A. susceptibility for crack propagation. Gases containing straight or branched chain hydrocarbons are expected to reduce the absorption potential ...fracture strength. Most optical- fibers currently in service have a composition that varies continuously from a Ucore of mixed GeO2 - Sio2 composit

  15. In situ synthesis and hydrothermal crystallization of nanoanatase TiO2 -SiO2 coating on aramid fabric (HTiSiAF) for UV protection.

    PubMed

    Deng, Hui; Zhang, Hongda

    2015-10-01

    TiO2 -SiO2 thin film was prepared by sol-gel method and coated on the aramid fabric to prepare functional textiles. The aramid fabric was dipped and withdrawn in TiO2 -SiO2 gel and hydrothermal crystallization at 80(°) C, then its UV protection functionality was evaluated. The crystalline phase and the surface morphology of TiO2 -SiO2 thin film were characterized using SEM, XRD, and AFM respectively. SEM showed hydrothermal crystallization led to a homogeneous dispersion of anatase nonocrystal in TiO2 -SiO2 film, and XRD suggested the mean particle size of the formed anatase TiO2 was less than 30 nm. AFM indicated that hydrothermal treatment enhanced the crystallization of TiO2 . UV protection analysis suggested that the hydrothermally treated coated textile had a better screening property in comparison with TiO2 -SiO2 gel and native aramid fabric.

  16. Sputtered SiO2 as low acoustic impedance material for Bragg mirror fabrication in BAW resonators.

    PubMed

    Olivares, Jimena; Wegmann, Enrique; Capilla, José; Iborra, Enrique; Clement, Marta; Vergara, Lucía; Aigner, Robert

    2010-01-01

    In this paper we describe the procedure to sputter low acoustic impedance SiO(2) films to be used as a low acoustic impedance layer in Bragg mirrors for BAW resonators. The composition and structure of the material are assessed through infrared absorption spectroscopy. The acoustic properties of the films (mass density and sound velocity) are assessed through X-ray reflectometry and picosecond acoustic spectroscopy. A second measurement of the sound velocity is achieved through the analysis of the longitudinal lambda/2 resonance that appears in these silicon oxide films when used as uppermost layer of an acoustic reflector placed under an AlN-based resonator.

  17. Molecular-Orientation-Induced Rapid Roughening and Morphology Transition in Organic Semiconductor Thin-Film Growth

    PubMed Central

    Yang, Junliang; Yim, Sanggyu; Jones, Tim S.

    2015-01-01

    We study the roughening process and morphology transition of organic semiconductor thin film induced by molecular orientation in the model of molecular semiconductor copper hexadecafluorophthalocyanine (F16CuPc) using both experiment and simulation. The growth behaviour of F16CuPc thin film with the thickness, D, on SiO2 substrate takes on two processes divided by a critical thickness: (1) D ≤ 40 nm, F16CuPc thin films are composed of uniform caterpillar-like crystals. The kinetic roughening is confirmed during this growth, which is successfully analyzed by Kardar-Parisi-Zhang (KPZ) model with scaling exponents α = 0.71 ± 0.12, β = 0.36 ± 0.03, and 1/z = 0.39 ± 0.12; (2) D > 40 nm, nanobelt crystals are formed gradually on the caterpillar-like crystal surface and the film growth shows anomalous growth behaviour. These new growth behaviours with two processes result from the gradual change of molecular orientation and the formation of grain boundaries, which conversely induce new molecular orientation, rapid roughening process, and the formation of nanobelt crystals. PMID:25801646

  18. Molecular-orientation-induced rapid roughening and morphology transition in organic semiconductor thin-film growth.

    PubMed

    Yang, Junliang; Yim, Sanggyu; Jones, Tim S

    2015-03-24

    We study the roughening process and morphology transition of organic semiconductor thin film induced by molecular orientation in the model of molecular semiconductor copper hexadecafluorophthalocyanine (F16CuPc) using both experiment and simulation. The growth behaviour of F16CuPc thin film with the thickness, D, on SiO2 substrate takes on two processes divided by a critical thickness: (1) D ≤ 40 nm, F16CuPc thin films are composed of uniform caterpillar-like crystals. The kinetic roughening is confirmed during this growth, which is successfully analyzed by Kardar-Parisi-Zhang (KPZ) model with scaling exponents α = 0.71 ± 0.12, β = 0.36 ± 0.03, and 1/z = 0.39 ± 0.12; (2) D > 40 nm, nanobelt crystals are formed gradually on the caterpillar-like crystal surface and the film growth shows anomalous growth behaviour. These new growth behaviours with two processes result from the gradual change of molecular orientation and the formation of grain boundaries, which conversely induce new molecular orientation, rapid roughening process, and the formation of nanobelt crystals.

  19. Interfacial SiO2 scavenging kinetics in HfO2 gate stack

    NASA Astrophysics Data System (ADS)

    Li, Xiuyan; Nishimura, Tomonori; Toriumi, Akira

    2016-11-01

    In this paper, Si and oxygen diffusions as well as SiO2 reduction reaction in HfO2/SiO2/Si stacks are examined in detail for fully understanding the SiO2-IL scavenging process. A 29Si isotope tracing experiment confirms that Si in SiO2-IL is mostly emitted from the HfO2 surface. In addition, the reaction of oxygen from SiO2 with VO in HfO2 is suggested. Furthermore, it is reported that the Si substrate is not changed at all in the SiO2-IL scavenging by simultaneously comparing a Si surface between with and without scavenged parts. Based on these results, a kinetic model for the SiO2-IL scavenging in HfO2/SiO2/Si stacks is proposed.

  20. Photoemission study on electrical dipole at SiO2/Si and HfO2/SiO2 interfaces

    NASA Astrophysics Data System (ADS)

    Fujimura, Nobuyuki; Ohta, Akio; Ikeda, Mitsuhisa; Makihara, Katsunori; Miyazaki, Seiichi

    2017-04-01

    Electrical dipole at SiO2/Si and HfO2/SiO2 interfaces have been investigated by X-ray photoelectron spectroscopy (XPS) under monochromatized Al Kα radiation. From the analysis of the cut-off energy for secondary photoelectrons measured at each thinning step of a dielectric layer by wet-chemical etching, an abrupt potential change caused by electrical dipole at SiO2/Si and HfO2/SiO2 interfaces has been clearly detected. Al-gate MOS capacitors with thermally-grown SiO2 and a HfO2/SiO2 dielectric stack were fabricated to evaluate the Al work function from the flat band voltage shift of capacitance–voltage (C–V) characteristics. Comparing the results of XPS and C–V measurements, we have verified that electrical dipole formed at the interface can be directly measured by photoemission measurements.

  1. Magnetization and anomalous Hall effect in SiO2/Fe/SiO2 trilayers

    NASA Astrophysics Data System (ADS)

    Sekhar Das, Sudhansu; Senthil Kumar, M.

    2017-03-01

    SiO2/Fe/SiO2 sandwich structure films fabricated by sputtering were studied by varying the Fe layer thickness (t Fe). The structural and microstructural studies on the samples showed that the Fe layer has grown in nanocrystalline form with (1 1 0) texture and that the two SiO2 layers are amorphous. Magnetic measurements performed with the applied field in in-plane and perpendicular direction to the film plane confirmed that the samples are soft ferromagnetic having strong in-plane magnetic anisotropy. The temperature dependence of magnetization shows complex behavior with the coexistence of both ferromagnetic and superparamagnetic properties. The transport properties of the samples as studied through Hall effect measurements show anomalous Hall effect (AHE). An enhancement of about 14 times in the saturation anomalous Hall resistance (R\\text{hs}\\text{A} ) was observed upon reducing the t Fe from 300 to 50 Å. The maximum value of R\\text{hs}\\text{A}   =  2.3 Ω observed for t Fe  =  50 Å sample is about 4 orders of magnitude larger than that reported for bulk Fe. When compared with the single Fe film, a maximum increase of about 56% in the R\\text{hs}\\text{A} was observed in sandwiched Fe (50 Å) film. Scaling law suggests that the R s follows the longitudinal resistivity (ρ) as, {{R}\\text{s}}\\propto {ρ1.9} , suggesting side jump as the dominant mechanism of the AHE. A maximum enhancement of about 156% in the sensitivity S was observed.

  2. Characteristics of the Electromagnetic Wave Absorbers of Composites Made of Ni-Zn Ferrite and Isolated SiO2 Particles

    NASA Astrophysics Data System (ADS)

    Kusunoki, Hiroki; Hiraki, Kiyohiro; Kondo, Takatoshi; Takada, Kazushi; Yoshikado, Shinzo

    It is found from simulation study that electromagnetic wave absorbers made of composites of Ni-Zn ferrite and SiO2 particles, which are mutually isolated each other in the continuous medium of Ni-Zn ferrite, show absorption in the frequency region both below and above 1GHz. The spray method is proposed to fabricate such composites in this study. The thin films of Ni-Zn ferrite can be coated on the surface of SiO2 particles by the spray thin film deposition method. It is confirmed by XRD and the electromagnetic characteristics measurement. The measured complex permeability approached to the calculated result using the isolation model of SiO2 particles in the Ni-Zn ferrite medium than using Lichtenecker’s logarithm mixed low.

  3. PECVD of nanostructured SiO2 in a modulated microwave plasma jet at atmospheric pressure

    NASA Astrophysics Data System (ADS)

    Hnilica, J.; Schäfer, J.; Foest, R.; Zajíčková, L.; Kudrle, V.

    2013-08-01

    Atmospheric pressure plasma enhanced chemical vapour deposition (AP-PECVD) of thin films by means of a microwave plasma jet operating with mixtures of argon and tetrakis(trimethylsilyloxy)silane (TTMS) is reported for the first time. In contrast to other siloxy-alkanes that are commonly used for PECVD, the molecule of TTMS (C12H36O4Si5) exhibits a complex and symmetric molecular structure which is presumably essential for a large scale nanostructuring of the films. Deposited films have been characterized by means of electron microscopy (SEM), x-ray spectroscopy (EDX), and infra-red spectroscopy (FTIR). The applied methods demonstrate the prevalent inorganic SiO2-like character of the films and their highly fractalized nanostructure over a wide range of dimension 100-104 nm. Contact angle measurements show the superhydrophobicity of the films, while the dispersive component of the surface energy can be varied in a controlled way by low-frequency amplitude modulation of the excitation power of the MW discharge. The modulation regimes of the jet have been investigated by means of time-resolved optical emission spectroscopy in order to describe the oscillations of plasma parameters e.g. rotational temperature from OH and relative emission of silicon atoms to substantiate the reproducibility of the deposition conditions and to correlate the plasma properties with the resulting film properties.

  4. A visual and organic vapor sensitive photonic crystal sensor consisting of polymer-infiltrated SiO2 inverse opal.

    PubMed

    Zhang, Yuqi; Qiu, Jianhua; Hu, Rongrong; Li, Pei; Gao, Loujun; Heng, Liping; Tang, Ben Zhong; Jiang, Lei

    2015-04-21

    A photonic crystal (PC) sensor that can selectively detect organic vapors through visual color changes has been proposed. The sensor was fabricated by infiltrating a tetraphenylethene polymer (TPEP) into the voids of SiO2 inverse opal photonic crystal. When the sensor was exposed to tetrahydrofuran or acetone vapor, a red shift of the stopband of more than 50 nm could be clearly observed; meanwhile, the film's color changed from violet to cyan. Subsequently, when exposed to air, the stopband underwent a blue shift and the color returned to violet. The reason for the observed change is that a reversible adsorption-desorption process occurs on alternate exposure of the sensor to organic vapor and air, due to the high specific surface area of the inverse opal macroporous structure and the high affinity of TPEP to tetrahydrofuran and acetone. The adsorption of vapor analyte can increase the PC's effective refractive index, which will induce the stopband red shift and the resulting color change according to Bragg's Law. The reversible adsorption-desorption of organic vapors varied the effective refractive index of the sensor repeatedly, causing the reversible stopband shift and color change, and providing a general method for the design of visual vapor sensors.

  5. Stress and environmental shift characteristics of HfO2/SiO2 multilayer coatings

    NASA Astrophysics Data System (ADS)

    Anzellotti, J. F.; Smith, Douglas J.; Sczupak, Robert J.; Chrzan, Z. Roman

    1997-05-01

    HfO2/SiO2 polarizer coatings for 1054 nm have been produced that have low stress at explicit environmental conditions without the employment of backside stress- compensation films. In this process hafnia is condensed from a metallic melt and silica from an oxide source, both via electron-beam evaporation. Specifically, this process has been adopted for multilayer designs with stringent requirements on spectral control and wavefront distortion. Efforts to meet these requirements have prompted various investigations of coating stress and spectral behavior, especially under changing environmental conditions. Results have shown that coating stress and optical thickness vary significantly with humidity. THese quantities have been measured under both ambient air and dry nitrogen atmospheres. The effects of coating parameters on stress and environmental stability have been examined for an experimental hafnia/silica polarizer coating. The aforementioned parameters are hafnia deposition rate, oxygen pressure during hafnia deposition, and oxygen pressure during silica deposition. Results indicate a strong correlation of coating stress to oxygen pressure during the silica evaporation. Data on the aging of stress in hafnia/silica coatings will also be presented. The HfO2/SiO2 process has ben utilized in high-laser-damage- threshold coatings for the OMEGA laser system and for National Ignition Facility development coatings at the Laboratory for Laser Energetics.

  6. Characterization of reactive ion etching of sol-gel SiO2 using Taguchi optimization method

    NASA Astrophysics Data System (ADS)

    Wee, Terence C.; Ooi, Boon Siew; Zhou, Yan; Chan, Yuen Chuen; Lam, Yee Loy

    1999-11-01

    SiO2 films prepared using sol-gel technique have found enormous potential applications in photonics, electronics and sensor devices. However, the feasibility of the devices utilizing sol-gel technology lies on the ease of the fabrication processes such as patterns transfer using wet or dry etchings. Dry etching is preferred over wet etching as it is able to produce finer features with high anisotropic etch profile. In this paper, we report the development of a dry reactive ion etching process for sol-gel SiO2 using a mixture of CF4 and O2 plasma. Parameters such as RF power, chamber pressure, CF4 and O2 flow rate, were optimized using a statistical method called Taguchi Technique. Etch rate of as high as 50nm/min, with high anisotropy etched profile, has been obtained.

  7. Wetting properties of phospholipid dispersion on tunable hydrophobic SiO2-glass plates.

    PubMed

    Alexandrova, Lidia; Karakashev, Stoyan I; Grigorov, L; Phan, Chi M; Smoukov, Stoyan K

    2015-06-01

    We study the wetting properties of very small droplets of salty aqueous suspensions of unilamellar liposomes of DMPC (dimyristoylphosphatidylcholine), situated on SiO2-glass surfaces with different levels of hydrophobicity. We evaluated two different measures of hydrophobicity of solid surfaces - receding contact angles and the thickness of wetting films trapped between an air bubble and the solid surface at different levels of hydrophobicity. We established a good correlation between methods which differ significantly in measurement difficulty and experimental setup. We also reveal details of the mechanism of wetting of different surfaces by the DMPC liposome suspension. Hydrophilic surfaces with water contact angles in the range of 0° to 35° are readily hydrophobized by the liposomes and only showed corresponding contact angles in the range 27°-43°. For same range of surface hydrophobicities, there was a clear reduction of the thickness of the wetting films between the surface and a bubble, reaching a minimum in the 35°-40° range. At higher levels of hydrophobicity both pure water and the liposome suspension show similar contact angles, and the thickness of wetting films between a bubble and those surfaces increases in parallel. Our analysis showed that the only force able to stabilize the film under these experimental conditions is steric repulsion. The latter suggests that nanobubbles adsorbed on hydrophobic parts of the surface, and coated with a DMPC layer, may be the cause of the 40-70 nm thickness of wetting films we observe.

  8. Suppression of photo-bias induced instability for amorphous indium tungsten oxide thin film transistors with bi-layer structure

    NASA Astrophysics Data System (ADS)

    Liu, Po-Tsun; Chang, Chih-Hsiang; Chang, Chih-Jui

    2016-06-01

    This study investigates the instability induced by bias temperature illumination stress (NBTIS) for an amorphous indium-tungsten-oxide thin film transistor (a-IWO TFT) with SiO2 backchannel passivation layer (BPL). It is found that this electrical degradation phenomenon can be attributed to the generation of defect states during the BPL process, which deteriorates the photo-bias stability of a-IWO TFTs. A method proposed by adding an oxygen-rich a-IWO thin film upon the a-IWO active channel layer could effectively suppress the plasma damage to channel layer during BPL deposition process. The bi-layer a-IWO TFT structure with an oxygen-rich back channel exhibits superior electrical reliability of device under NBTIS.

  9. The application of Cu/SiO2 catalytic system in chemical mechanical planarization based on the stability of SiO2 sol

    NASA Astrophysics Data System (ADS)

    Yan, Li; Yuling, Liu; Aochen, Wang; Zhixin, Yang; Mingbin, Sun; Chuan, Cheng; Yufeng, Zhang; Nannan, Zhang

    2014-06-01

    There is a lot of hydroxyl on the surface of nano SiO2 sol used as an abrasive in the chemical mechanical planarization (CMP) process, and the chemical reaction activity of the hydroxyl is very strong due to the nano effect. In addition to providing a mechanical polishing effect, SiO2 sol is also directly involved in the chemical reaction. The stability of SiO2 sol was characterized through particle size distribution, zeta potential, viscosity, surface charge and other parameters in order to ensure that the chemical reaction rate in the CMP process, and the surface state of the copper film after CMP was not affected by the SiO2 sol. Polarization curves and corrosion potential of different concentrations of SiO2 sol showed that trace SiO2 sol can effectively weaken the passivation film thickness. In other words, SiO2 sol accelerated the decomposition rate of passive film. It was confirmed that the SiO2 sol as reactant had been involved in the CMP process of copper film as reactant by the effect of trace SiO2 sol on the removal rate of copper film in the CMP process under different conditions. In the CMP process, a small amount of SiO2 sol can drastically alter the chemical reaction rate of the copper film, therefore, the possibility that Cu/SiO2 as a catalytic system catalytically accelerated the chemical reaction in the CMP process was proposed. According to the van't Hoff isotherm formula and the characteristics of a catalyst which only changes the chemical reaction rate with out changing the total reaction standard Gibbs free energy, factors affecting the Cu/SiO2 catalytic reaction were derived from the decomposition rate of Cu (OH)2 and the pH value of the system, and then it was concluded that the CuSiO3 as intermediates of Cu/SiO2 catalytic reaction accelerated the chemical reaction rate in the CMP process. It was confirmed that the Cu/SiO2 catalytic system generated the intermediate of the catalytic reaction (CuSiO3) in the CMP process through the removal

  10. Bacterial adherence to SiO2-based multifunctional bioceramics.

    PubMed

    Kinnari, Teemu J; Esteban, Jaime; Gomez-Barrena, Enrique; Zamora, Nieves; Fernandez-Roblas, Ricardo; Nieto, Alejandra; Doadrio, Juan C; López-Noriega, Adolfo; Ruiz-Hernández, Eduardo; Arcos, Daniel; Vallet-Regí, María

    2009-04-01

    The bacterial adherence onto different multifunctional silica-based bioceramics has been evaluated. Staphylococcus aureus and Staphylococcus epidermidis were chosen, as they cause the majority of the implant-related infections in this field. Two SiO2 mesoporous materials (MCM-41, SBA-15), an ordered SiO2-CaO-P2O5 mesoporous glass (OMG), and a biphasic magnetic bioceramic (BMB), were incubated with S. aureus and S. epidermidis for 90 min, and subsequently sonicated to quantify the number of adhered bacteria on each material. It was found that S. aureus and S. epidermidis (10(8) CFU/mL) adhered significantly less to BMB samples when compared to MCM-41, SBA-15, or OMG. However, when the material pores accessible for bacteria in each material were taken into account, the lowest bacterial adherence was found in MCM-41, and the highest in SBA-15. The results show that bacterial adherence is higher on mesoporous bioceramics, although this higher microbial attachment is mainly due to the intergranular porosity and grain size morphology rather than to the mesoporous structure.

  11. Defect Dynamics in the Network Glass SiO2

    NASA Astrophysics Data System (ADS)

    Vollmayr-Lee, Katharina; Zippelius, Annette

    2014-03-01

    We study the dynamics of the strong glass former SiO2 via molecular dynamics simulations below the glass transition temperature. To focus on microscopic processes, we average single particle trajectories over time windows of about 100 particle oscillations. The structure on this coarse-grained time scale is very well defined in terms of coordination numbers, allowing us to identify ill-coordinated atoms, called defects in the following. The most numerous defects are O-O neighbors, whose lifetimes are comparable to the equilibration time at low temperature. On the other hand SiO and OSi defects are very rare and short lived. The lifetime of defects is found to be strongly temperature dependent, consistent with activated processes. Single-particle jumps give rise to local structural rearrangements. We show that in SiO2 these structural rearrangements are coupled to the creation or annihilation of defects, giving rise to very strong correlations of jumping atoms and defects. This project was funded by the Deutsche Forschungsgemeinschaft via SFB 602 and FOR 1394.

  12. Avalanches in compressed porous SiO(2)-based materials.

    PubMed

    Nataf, Guillaume F; Castillo-Villa, Pedro O; Baró, Jordi; Illa, Xavier; Vives, Eduard; Planes, Antoni; Salje, Ekhard K H

    2014-08-01

    The failure dynamics in SiO(2)-based porous materials under compression, namely the synthetic glass Gelsil and three natural sandstones, has been studied for slowly increasing compressive uniaxial stress with rates between 0.2 and 2.8 kPa/s. The measured collapsed dynamics is similar to Vycor, which is another synthetic porous SiO(2) glass similar to Gelsil but with a different porous mesostructure. Compression occurs by jerks of strain release and a major collapse at the failure point. The acoustic emission and shrinking of the samples during jerks are measured and analyzed. The energy of acoustic emission events, its duration, and waiting times between events show that the failure process follows avalanche criticality with power law statistics over ca. 4 decades with a power law exponent ɛ≃ 1.4 for the energy distribution. This exponent is consistent with the mean-field value for the collapse of granular media. Besides the absence of length, energy, and time scales, we demonstrate the existence of aftershock correlations during the failure process.

  13. Additivity of kinetic and potential energy contributions in modification of graphene supported on SiO2

    NASA Astrophysics Data System (ADS)

    Zhang, Xitong; Zhao, Shijun; Wang, Yuyu; Xue, Jianming

    2017-04-01

    The damage production induced by MeV highly charged ions (HCI) irradiations in graphene supported on a SiO2 substrate is investigated using molecular dynamics method. We get results in agreement with our recent experiments. We find that the electronic energy loss and potential energy deposition have similar effects on the defects creation in SiO2 substrate-supported graphene and both mechanisms of energy deposition seem to contribute in an additive way. The influences of the energy deposition depth and radius are studied. Only the energy deposited below the surface within 2.5 nm will induce the damage in graphene. Hence, the HCI can be a powerful tool to induce defects in graphene without causing deep damage of the substrate. When charge of incident Xeq+ is above 30, a nanopore is formed and the size of nanopore in graphene can be controlled by changing the incident charge state.

  14. Engineered magnetic core-shell SiO2/Fe microspheres and "medusa-like" microspheres of SiO2/iron oxide/carbon nanofibers or nanotubes.

    PubMed

    Mero, On; Sougrati, Moulay-Tahar; Jumas, Jean-Claude; Margel, Shlomo

    2014-08-19

    Iron oxide (IO) thin coatings of controlled thickness on SiO2 microspheres of narrow size distribution were prepared by decomposition at 160 °C of triiron dodecacarbonyl onto silica microspheres dispersed in diethylene glycol diethyl ether free of surfactant or stabilizer. The dried washed SiO2/IO core-shell microspheres were annealed at different temperatures and time periods under inert (Ar) or reducing (H2) atmosphere. The effect of temperature on the chemical composition, morphology, crystallinity, and magnetic properties of the IO and the elemental Fe nanoparticles type coatings onto the SiO2 core microspheres has been elucidated. "Medusa-like" SiO2/IO/carbon nanofibers and tubes particles were prepared by CVD of ethylene on the surface of the SiO2/IO microspheres at different temperatures. The morphology change of the grafted carbon nanofibers and tubes as a function of the CVD temperature was also elucidated.

  15. Niobium oxide dispersed on a carbon-ceramic matrix, SiO2/C/Nb2O5, used as an electrochemical ascorbic acid sensor.

    PubMed

    Arenas, Leliz T; Villis, Paulo C M; Arguello, Jacqueline; Landers, Richard; Benvenutti, Edilson V; Gushikem, Yoshitaka

    2010-11-15

    A film of niobium oxide was immobilized on a SiO(2)/C carbon-ceramic matrix (specific surface area 270 m(2)g(-1)) and characterized by N(2) adsorption-desorption isotherms, scanning electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. This new carbon-ceramic material, SiO(2)/C/Nb(2)O(5), was used for construction of electrodes, and it shows ability to improve the electron-transfer between the electrode surface and ascorbic acid. The electrocatalytic oxidation of ascorbic acid was made by differential pulse and cyclic voltammetry techniques, making it potentially useful for developing a new ascorbic acid sensor.

  16. Ge nanocrystals embedded in ultrathin Si3N4 multilayers with SiO2 barriers

    NASA Astrophysics Data System (ADS)

    Bahariqushchi, R.; Gundogdu, Sinan; Aydinli, A.

    2017-04-01

    Multilayers of germanium nanocrystals (NCs) embedded in thin films of silicon nitride matrix separated with SiO2 barriers have been fabricated using plasma enhanced chemical vapor deposition (PECVD). SiGeN/SiO2 alternating bilayers have been grown on quartz and Si substrates followed by post annealing in Ar ambient from 600 to 900 °C. High resolution transmission electron microscopy (HRTEM) as well as Raman spectroscopy show good crystallinity of Ge confined to SiGeN layers in samples annealed at 900 °C. Strong compressive stress for SiGeN/SiO2 structures were observed through Raman spectroscopy. Size, as well as NC-NC distance were controlled along the growth direction for multilayer samples by varying the thickness of bilayers. Visible photoluminescence (PL) at 2.3 and 3.1 eV with NC size dependent intensity is observed and possible origin of PL is discussed.

  17. Effect of Different TiO2-SiO2 Multilayer Coatings Applied by Sol-Gel Method on Antireflective Property

    NASA Astrophysics Data System (ADS)

    lari, Najme; Ahangarani, Shahrokh; Shanaghi, Ali

    2015-07-01

    Multilayer thin films prepared using the sol-gel process have been used in many antireflection applications. In this paper, antireflective nanoscale multilayer TiO2-SiO2 coatings were formed on both sides of the glass substrates by combining sol-gel method and dip coating techniques. The coatings were carried out using tetraethyl orthosilicate as precursor for SiO2 and tetrabutyl orthotitanate as precursor for TiO2. The coatings prepared in this work were characterized using scanning electron microscope, Fourier-transformed infrared spectrophotometer and UV-Visible spectrophotometer. The SiO2 top layer coatings showed excellent antireflection in the wavelength range of 400-800 nm where the transmittance of glass substrate is significantly lower. By increasing the number of double TiO2-SiO2 layers, the transmission of the coated glasses increased due to applied multilayer coating properties. Six-layer sol-gel TiO2-SiO2 coatings showed the highest visible transmittance about 99.25% at the band of 550-650 nm.

  18. Close-packed SiO 2/poly(methyl methacrylate) binary nanoparticles-coated polyethylene separators for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Park, Jang-Hoon; Cho, Joo-Hyun; Park, Woong; Ryoo, Dongjo; Yoon, Su-Jin; Kim, Jong Hun; Jeong, Yeon Uk; Lee, Sang-Young

    In an endeavour to improve not only the thermal shrinkage but also the electrochemical performance of separators in lithium-ion batteries, a novel composite separator is developed, i.e., a close-packed SiO 2/poly(methyl methacrylate) (PMMA) binary nanoparticles-coated polyethylene (PE) separator. The introduction of SiO 2 nanoparticles to the coating layer effectively suppresses thermal shrinkage of the composite separator. In contrast to a SiO 2/PMMA coating layer having a film-shaped PMMA binder, the SiO 2/PMMA binary nanoparticle coating layer employs PMMA particles as a binder. As a consequence, a highly porous structure, i.e., well-connected interstitial voids, is formed between the binary SiO 2 and PMMA nanoparticles. The unique porous morphology allows favourable liquid electrolyte wettability and facile ionic conduction, which play a crucial role in improving cell performance such as the discharge capacity and the C-rate capability of the composite separator.

  19. Observation of electron trapping along scratches on SiO2 surface in mirror electron microscope images under ultraviolet light irradiation

    NASA Astrophysics Data System (ADS)

    Hasegawa, Masaki; Shimakura, Tomokazu

    2010-04-01

    Surface charge distribution change caused by electrons trapped at defects of a SiO2 surface has been observed by using a mirror electron microscope (MEM) under monochromatized ultraviolet (UV) light irradiation. Scratches on the SiO2 surface on a silicon wafer were formed by mechanically polishing to create spatially distributed defects on the SiO2 surface. Exposure of the SiO2 surface by UV light with energy above 4.25 eV, which is the threshold energy for internal photoemission from silicon to SiO2, produced significant change in the contrast in the MEM images. This contrast change is mainly due to negative charging by the photoexcited electrons trapped at the defects along the scratches. The negative charging changes the curvature of the electrostatic equipotential surface above the scratches from a concave shape to a convex shape; as a result, their contrast in the MEM image becomes reversed. The surface density of the trapped electrons at a typical scratch was roughly estimated to be 1010 cm-2. This result of analysis of the contrast change shows that the MEM can be used for spatially resolved and spectroscopic characterizations of defects relating charge trapping in insulator films in conjunction with a charge-injection technique such as UV irradiation.

  20. Direct fabrication of hybrid nanofibres composed of SiO2-PMMA nanospheres via electrospinning.

    PubMed

    Zhang, Ran; Shang, Tinghua; Yang, Guang; Jia, Xiaolong; Cai, Qing; Yang, Xiaoping

    2016-08-01

    The direct fabrication of hybrid nanofibres composed of poly(methyl methacrylate)-grafted SiO2 (SiO2-PMMA) nanospheres via electrospinning was investigated in detail. SiO2-PMMA nanospheres were successfully prepared, with the SiO2 nanospheres synthesized via the Stober method, followed by in situ surface-initiated atom transfer radical polymerization of methyl methacrylate (MMA). Electrospinning was carried out with N,N-dimethylformamide (DMF) as the solvent to disperse SiO2-PMMA nanospheres. The size of the SiO2 core, the molecular weight of the PMMA shell and the concentration of the SiO2-PMMA/DMF solution all had substantial effects on the morphology and structure of electrospun nanofibres composed of SiO2-PMMA nanospheres. When these determining factors were well-tailored, it was found that one-dimensional necklace-like nanofibres were obtained, with SiO2-PMMA nanospheres aligned one by one along the fibre. The successful fabrication of nanofibres by directly electrospinning the SiO2-PMMA/DMF solution verified that polymer-grafted particles possess polymer-like characteristics, which endowed them with the ability to be processed into desirable shapes and structures.

  1. HfO2/SiO2 multilayer based reflective and transmissive optics from the IR to the UV

    NASA Astrophysics Data System (ADS)

    Wang, Jue; Hart, Gary A.; Oudard, Jean Francois; Wamboldt, Leonard; Roy, Brian P.

    2016-05-01

    HfO2/SiO2 multilayer based reflective optics enable threat detection in the short-wave/middle-wave infrared and high power laser targeting capability in the near infrared. On the other hand, HfO2/SiO2 multilayer based transmissive optics empower early missile warning by taking advantage of the extremely low noise light detection in the deep-ultraviolet region where solar irradiation is strongly absorbed by the ozone layer of the earth's atmosphere. The former requires high laser damage resistance, whereas the latter needs a solar-blind property, i.e., high transmission of the radiation below 290 nm and strong suppression of the solar background from 300 nm above. The technical challenges in both cases are revealed. The spectral limits associated with the HfO2 and SiO2 films are discussed and design concepts are schematically illustrated. Spectral performances are realized for potential A and D and commercial applications.

  2. XPS study of interface formation of CVD SiO2 on InSb. [X-ray Photoemission Spectroscopy

    NASA Technical Reports Server (NTRS)

    Vasquez, R. P.; Grunthaner, F. J.

    1981-01-01

    The interfacial chemistry of CVD SiO2 films deposited on thin native oxides grown on InSb substrates is examined using X-ray photoemission spectroscopy (XPS) and a relatively benign chemical etching technique for depth profiling. An intensity analysis of XPS spectra is used to derive the compositional structure of the interfaces obtained in the SiO2/native oxide/InSb system. Peak positions in these spectra are used to follow the change in substrate surface potential during the etch sequence, and to establish the chemical nature of the species formed during deposition and subsequent processing. Reaction of the substrate with oxygen resulted in an In-rich native oxide and 1-2 monolayers of excess elemental Sb at the native-oxide/substrate interface, incompletely oxidized silane reduced the native oxide, leaving less than 1 monolayer of elemental In at the SiO2/native oxide interface. Etch removal of this thin In-rich layer leads to a change in the substrate surface potential of 0.06 eV, corresponding to a net increase in positive charge. The results are consistent with simple thermodynamic considerations; they are also compared to previously reported studies of deposited dielectrics on III-V compound semiconductors.

  3. Origin and removal of stacking faults in Ge islands nucleated on Si within nanoscale openings in SiO2

    NASA Astrophysics Data System (ADS)

    Leonhardt, Darin; Ghosh, Swapnadip; Han, Sang M.

    2011-10-01

    We have previously reported that Ge films formed after nucleation of Ge islands within nanometer size openings in SiO2 and their subsequent coalescence over the SiO2 template exhibit threading dislocation densities below 106 cm-2. However, these films contain a density of twin/stacking fault defects on the order of 5 × 1010 cm-2 that emanate primarily from the Ge-SiO2 interface. Most of these faults self-terminate within 200 nm of the interface; however, a total of 5 × 107 cm-2 propagate to the Ge surface. These defects are found to be detrimental to the morphology and minority carrier lifetime in III-V films integrated onto the Ge-on-Si virtual substrates. We have found that annealing the Ge islands during the initial stage of coalescence eliminates stacking faults, but further Ge growth leads to a film containing a threading dislocation density of 5 × 107 cm-2. To explain the origin of the twin/stacking fault defects in the Ge films and their removal after annealing Ge islands, we have studied the Ge islands before and after annealing. Our results indicate that twin/stacking faults originate from Ge islands that nucleate within nanoscale windows in the SiO2 template, in twin relationship to the underlying Si, and their coalescence with other epitaxial Ge islands. The density of Ge islands in twin relationship is approximately 4 × 1010 cm-2. In addition to the twin-oriented Ge islands, we observe that another group of Ge islands on the order of 2 × 1010 cm-2 have a small tilt-misorientation to the underlying Si ranging from 1.8 to 5.6°. After annealing, the density of both epitaxial and twin-oriented Ge islands is significantly reduced, and only the tilt-misoriented islands remain. The reduction in epitaxial and twin-oriented Ge islands stems from the thermal desorption of SiO2 template during the annealing, which leads to the transfer of Ge by surface diffusion from these Ge islands to the freshly exposed Si. This surface diffusion, while causing

  4. In vitro and in vivo genotoxicity investigations of differently sized amorphous SiO2 nanomaterials.

    PubMed

    Maser, Elena; Schulz, Markus; Sauer, Ursula G; Wiemann, Martin; Ma-Hock, Lan; Wohlleben, Wendel; Hartwig, Andrea; Landsiedel, Robert

    2015-12-01

    In vitro and in vivo genotoxic effects of differently sized amorphous SiO2 nanomaterials were investigated. In the alkaline Comet assay (with V79 cells), non-cytotoxic concentrations of 300 and 100-300μg/mL 15nm-SiO2 and 55nm-SiO2, respectively, relevant (at least 2-fold relative to the negative control) DNA damage. In the Alkaline unwinding assay (with V79 cells), only 15nm-SiO2 significantly increased DNA strand breaks (and only at 100μg/mL), whereas neither nanomaterial (up to 300μg/mL) increased Fpg (Formamidopyrimidine DNA glycosylase)-sensitive sites reflecting oxidative DNA base modifications. In the Comet assay using rat precision-cut lung slices, 15nm-SiO2 and 55nm-SiO2 induced significant DNA damage at ≥100μg/mL. In the Alkaline unwinding assay (with A549 cells), 30nm-SiO2 and 55nm-SiO2 (with larger primary particle size (PPS)) induced significant increases in DNA strand breaks at ≥50μg/mL, whereas 9nm-SiO2 and 15nm-SiO2 (with smaller PPS) induced significant DNA damage at higher concentrations. These two amorphous SiO2 also increased Fpg-sensitive sites (significant at 100μg/mL). In vivo, within 3 days after single intratracheal instillation of 360μg, neither 15nm-SiO2 nor 55nm-SiO2 caused genotoxic effects in the rat lung or in the bone marrow. However, pulmonary inflammation was observed in both test groups with findings being more pronounced upon treatment with 15nm-SiO2 than with 55nm-SiO2. Taken together, the study shows that colloidal amorphous SiO2 with different particle sizes may induce genotoxic effects in lung cells in vitro at comparatively high concentrations. However, the same materials elicited no genotoxic effects in the rat lung even though pronounced pulmonary inflammation evolved. This may be explained by the fact that a considerably lower dose reached the target cells in vivo than in vitro. Additionally, the different time points of investigation may provide more time for DNA damage repair after instillation.

  5. [Effect of PEG400 on the luminescent Eu(BA)3/SiO2].

    PubMed

    Zeng, Dong-ming; Li, Yan-hua; Fu, Chang-cheng; Liu, You-nian; Shu, Wan-gen

    2007-02-01

    Rare earth organic complexes combined with inorganic compounds can enhanced thermal stability, but inorganic compounds matrix has great influence on the luminescence characteristic of rare earth organic complexes. The luminescence characteristic of organic and inorganic compound material was improved by PEG doping in the material. Eu(BA)3/SiO2 and Eu(BA)3/PEG400-SiO2 were synthesized by Sol-Gel method. The result of luminescence analysis showed that the excitation spectra and emission spectra of Eu(BA)3 accorded with those of Eu(BA)3/SiO2 and Eu(BA)3/PEG400-SiO2, but the luminescence intensity of Eu(BA)3/SiO2 was improved by PEG400-SiO2 in SiO2 gel. This was because PEG400 as a hard Lewis base, could be combined with rare earth ion and increase the luminescence intensity of Eu(BA)3. It was shown that the amount of PEG400 in Eu(BA)3/SiO2 had influence on luminescence intensity of Eu(BA)3, namely there was better luminescence intensity in Eu(BA)3/SiO2 with increment of the PEG400 addition, but when the amount of PEG400 exceeded 50 wt% of that of SiO2, the luminescence intensity of Eu(BA)3 hardly increased. When the amount of PEG400 exceed 15 wt% of that of SiO2, PEG400 had little influence on the content of water and hydroxy in the matrix, as verified by IR spectrum. The surface characteristic of SiO2 gel was investigated by atomic force microscopy (AFM).

  6. Synthesis and catalytic performance of SiO2@Ni and hollow Ni microspheres

    NASA Astrophysics Data System (ADS)

    Liu, Xin; Liu, Yanhua; Shi, Xueting; Yu, Zhengyang; Feng, Libang

    2016-11-01

    Nickel (Ni) catalyst has been widely used in catalytic reducing reactions such as catalytic hydrogenation of organic compounds and catalytic reduction of organic dyes. However, the catalytic efficiency of pure Ni is low. In order to improve the catalytic performance, Ni nanoparticle-loaded microspheres can be developed. In this study, we have prepared Ni nanoparticle-loaded microspheres (SiO2@Ni) and hollow Ni microspheres using two-step method. SiO2@Ni microspheres with raspberry-like morphology and core-shell structure are synthesized successfully using SiO2 microsphere as a template and Ni2+ ions are adsorbed onto SiO2 surfaces via electrostatic interaction and then reduced and deposited on surfaces of SiO2 microspheres. Next, the SiO2 cores are removed by NaOH etching and the hollow Ni microspheres are prepared. The NaOH etching time does no have much influence on the crystal structure, shape, and surface morphology of SiO2@Ni; however, it can change the phase composition evidently. The hollow Ni microspheres are obtained when the NaOH etching time reaches 10 h and above. The as-synthesized SiO2@Ni microspheres exhibit much higher catalytic performance than the hollow Ni microspheres and pure Ni nanoparticles in the catalytic reduction of methylene blue. Meanwhile, the SiO2@Ni catalyst has high stability and hence it can be recycled for reuse.

  7. High-fidelity conformation of graphene to SiO2 topographic features.

    PubMed

    Cullen, W G; Yamamoto, M; Burson, K M; Chen, J H; Jang, C; Li, L; Fuhrer, M S; Williams, E D

    2010-11-19

    High-resolution noncontact atomic force microscopy of SiO2 reveals previously unresolved roughness at the few-nm length scale, and scanning tunneling microscopy of graphene on SiO2 shows graphene to be slightly smoother than the supporting SiO2 substrate. A quantitative energetic analysis explains the observed roughness of graphene on SiO2 as extrinsic, and a natural result of highly conformal adhesion. Graphene conforms to the substrate down to the smallest features with nearly 99% fidelity, indicating conformal adhesion can be highly effective for strain engineering of graphene.

  8. Carbon Diffusion through SiO2 from a Hydrogenated Amorphous Carbon Layer and Accumulation at the SiO2/Si Interface

    NASA Astrophysics Data System (ADS)

    Krafcsik, Olga H.; Vida, György; Pócsik, István; Josepovits, Katalin V.; Deák, Péter

    2001-04-01

    Carbon diffusion in a SiO2/Si system was investigated. The source was provided by chemical vapor deposition of a hydrogenated amorphous carbon layer onto the oxide at low temperature. From layers with low oxygen content, no carbon outdiffusion was detected up to 1190°C@. If the O content was high, the diffusion would start suddenly at 1140°C, and carbon accumulation would be found on the Si side of the SiO2/Si interface in the form of SiC precipitates. These results are interpreted by assuming oxygen-assisted dissociation of carbon atoms from the carbon layer in form of CO molecules, fast CO diffusion through SiO2 and an exothermic reaction of CO with Si. No carbon segregation was found in SiO2. Consequences of carbon island formation during SiC oxidation are pointed out.

  9. Fabrication of a metal-oxide-semiconductor-type capacitive microtip array using SiO2 or HfO2 gate insulators

    NASA Astrophysics Data System (ADS)

    Kim, Kyung-Min; Choi, Byung Joon; Kim, Seong Keun; Hwang, Cheol Seong

    2004-11-01

    Capacitive tip arrays having a metal-insulator-semiconductor capacitor structure were fabricated using thermally oxidized SiO2 or atomic-layer-deposited HfO2 gate dielectric films for their application to scanning-probe-array-type memory devices. The SiO2 film showed a nonuniform thickness distribution over the flat and tip areas of the arrays owing to the different oxidation speeds of the flat and tip Si surfaces. This resulted in a smaller sensing margin of the device. However, the high-dielectric HfO2 film showed not only a higher capacitance value but also a more uniform growth behavior over the whole area, which would result in a better device performance. The capacitance-voltage characteristics of both devices coincide well with the simulation results based on conventional metal-insulator-semiconductor theories.

  10. Controlling the nanoscale rippling of graphene with SiO2 nanoparticles.

    PubMed

    Osváth, Z; Gergely-Fülöp, E; Nagy, N; Deák, A; Nemes-Incze, P; Jin, X; Hwang, C; Biró, L P

    2014-06-07

    The electronic properties of graphene can be significantly influenced by mechanical strain. One practical approach to induce strain in graphene is to transfer atomically thin membranes onto pre-patterned substrates with specific corrugations. The possibility of using nanoparticles to impart extrinsic rippling to graphene has not been fully explored yet. Here we study the structure and elastic properties of graphene grown by chemical vapour deposition and transferred onto a continuous layer of SiO2 nanoparticles with diameters of around 25 nm, prepared on a Si substrate by the Langmuir-Blodgett technique. We show that the corrugation of the transferred graphene, and thus the membrane strain, can be modified by annealing at moderate temperatures. The membrane parts bridging the nanoparticles are suspended and can be reversibly lifted by the attractive forces between an atomic force microscope tip and graphene. This allows the dynamic control of the local morphology of graphene nanomembranes.

  11. Optical characterization of glutamate dehydrogenase monolayers chemisorbed on SiO2

    NASA Astrophysics Data System (ADS)

    Pompa, P. P.; Blasi, L.; Longo, L.; Cingolani, R.; Ciccarella, G.; Vasapollo, G.; Rinaldi, R.; Rizzello, A.; Storelli, C.; Maffia, M.

    2003-04-01

    This paper describes the formation of glutamate dehydrogenase monolayers on silicon dioxide, and their characterization by means of physical techniques, i.e., fluorescence spectroscopy and Fourier-transform infrared spectroscopy. Detailed investigations of the intrinsic stability of native proteins in solution were carried out to elucidate the occurrence of conformational changes induced by the immobilization procedure. The enzyme monolayers were deposited on SiO2 after preexposing silicon surfaces to 3-aminopropyltriethoxysilane and reacting the silylated surfaces with glutaric dialdehyde. The optical characterization demonstrates that the immobilization does not interfere with the fold pattern of the native enzyme. In addition, fluorescence spectroscopy, thermal denaturation, and quenching studies performed on the enzyme in solution well describe the folding and unfolding properties of glutamate dehydrogenase. The photophysical studies reported here are relevant for nanobioelectronics applications requiring protein immobilization on a chip.

  12. Lateral solidification of a liquid crystalline semiconductor film induced by temperature gradient

    NASA Astrophysics Data System (ADS)

    Hoshino, Tomoya; Ito, Hayato; Fujieda, Ichiro; Hanasaki, Tomonori

    2013-09-01

    Derivatives of [1]benzothieno[3,2-b]benzothiophene (BTBT) are attracting much attention as a highly soluble, highmobility semiconductor material for thin-film transistor applications. These small molecules are known to organize themselves into a single crystalline structure after spin coating or drop casting. Charge transport in a single crystal material is anisotropic in nature. Hence, it is desired to control its orientation during growth or recrystallization so that the source and drain electrodes of a transistor are to be placed along a faster transport direction. We propose to generate temperature gradient in a heated liquid crystalline thin film to induce lateral recrystallization. In experiment, we tried two methods. First, an aluminum plate with two narrow ridges was inserted between a temperature-controlled stage and a square silicon substrate with a 200nm-thick SiO2 and a spin-coated C8-BTBT film. We raised the temperature of the stage to 120oC and let it cool gradually. During cooling at around 105oC , the color of the sample started to change, indicating a phase change. This change proceeded from the corners of the film and in about 30 seconds, darker regions merged at the center of the substrate. Second, the sample was placed at the edge of the stage. In this case, the color change started from the protruding corner of the sample and proceeded toward the other end. Micrograph observation revealed that cracks were formed in these films and they were perpendicular to the direction of the phase change.

  13. Proton induced multilevel storage capability in self-assembled indium-zinc-oxide thin-film transistors

    NASA Astrophysics Data System (ADS)

    Guo, Li Qiang; Jin Wan, Chang; Qiang Zhu, Li; Wan, Qing

    2013-09-01

    Multilevel memory capability of self-assembled indium-zinc-oxide (IZO) electric-double-layer (EDL) thin-film transistors gated by nanogranular SiO2 proton conducting electrolytes is investigated. More than four distinct memory states are obtained by programming gate voltage. The observed multilevel storage behavior is mainly due to the controlled interfacial electrochemical doping of IZO channel by penetrated protons under programmed gate voltages. In addition, such IZO-based EDL transistor multilevel memory exhibits good characteristics of programming/erasing endurance and data retention. Such oxide-based EDL transistors with proton-induced multilevel memory behavior are interesting for low-cost memory and neuromorphic system applications after further properties and size optimization.

  14. Tetragonal to Cubic Transformation of SiO2-Stabilized ZrO2 Polymorph through Dysprosium Substitutions.

    PubMed

    Vasanthavel, Subramaniyan; Derby, Brian; Kannan, Sanjeevi

    2017-02-06

    Partially stabilized tetragonal zirconia (t-ZrO2) is of particular interest for hard tissue replacements. Aging-related failures of the ceramic associated with the gradual transformation from t-ZrO2 to m-ZrO2 (monoclinic zirconia) can lead to its premature removal from the implant site. In addition, monitoring the satisfactory performance of the implant throughout its lifespan without invasive techniques is a challenging task. The magnetic resonance imaging (MRI) contrast ability of dysprosium (Dy(3+)) is well-established. To this aim, varied levels of Dy(3+) additions in the ZrO2-SiO2 binary oxide system were explored. The results indicate the effective role of Dy(3+) in the formation of thermally and mechanically stable c-ZrO2 (cubic zirconia) phase at higher temperatures. The presence of SiO2 influenced the t-ZrO2 stabilization, whereas Dy(3+) tends to occupy the ZrO2 lattice sites to induce c-ZrO2 transition. Magnetic and MRI tests displayed the commendable contrast ability of Dy(3+) stabilized ZrO2-SiO2 binary systems. Nanoindentation results demonstrate a remarkable enhancement of the mechanical properties.

  15. Prediction of 10-fold coordinated TiO2 and SiO2 structures at multimegabar pressures

    PubMed Central

    Lyle, Matthew J.; Pickard, Chris J.; Needs, Richard J.

    2015-01-01

    We predict by first-principles methods a phase transition in TiO2 at 6.5 Mbar from the Fe2P-type polymorph to a ten-coordinated structure with space group I4/mmm. This is the first report, to our knowledge, of the pressure-induced phase transition to the I4/mmm structure among all dioxide compounds. The I4/mmm structure was found to be up to 3.3% denser across all pressures investigated. Significant differences were found in the electronic properties of the two structures, and the metallization of TiO2 was calculated to occur concomitantly with the phase transition to I4/mmm. The implications of our findings were extended to SiO2, and an analogous Fe2P-type to I4/mmm transition was found to occur at 10 TPa. This is consistent with the lower-pressure phase transitions of TiO2, which are well-established models for the phase transitions in other AX2 compounds, including SiO2. As in TiO2, the transition to I4/mmm corresponds to the metallization of SiO2. This transformation is in the pressure range reached in the interiors of recently discovered extrasolar planets and calls for a reformulation of the equations of state used to model them. PMID:25991859

  16. Effect of pressure on cation partitioning between immiscible liquids in the system Ti0 2-SiO 2

    NASA Astrophysics Data System (ADS)

    Circone, S.; Agee, C. B.

    1995-03-01

    Liquidus phase relations in the system Si0 2-TiO 2 have been determined at 3.0 GPa to investigate the effect of pressure on the partitioning of Si and Ti between coexisting immiscible liquids. Experiments on oxide mixtures containing 10, 50, 90, and 100 mol% TiO 2 were performed in multi-anvil and piston-cylinder apparatus at 2173-2740 K. At 1 atm, immiscible liquids form because the liquid structures are dissimilar: tetravalent cations occur in primarily fourfold (Si0 2-rich liquid) vs. sixfold (TiO 2-rich liquid) coordination by oxygen. At 3.0 GPa, immiscible liquids also coexist, but the phase relations and liquid compositions are significantly different. The eutectic liquid is now Ti0 2-rich (78.4 vs. 8.1 mol% TiO 2 at 1 atm). Above the liquidus, the coexisting immiscible liquids are enriched in Si0 2. The Si0 2 content of the TiO 2-rich liquid has increased by more than a factor of 3, while the TiO2-content of the SiO 2-rich liquid has decreased by 1/2. The persistence of a wide solvus implies that pressure does not cause liquid structure assimilation. The observed shift in immiscible liquid compositions indicated that pressure has raised the activity of TiO 2 in the liquid dominated by tetravalent cations in fourfold coordination and lowered the activity of SiO 2 in a liquid dominated by tetravalent cations in sixfold coordination. The decrease in TiO 2 content of the SiO 2-rich liquid with pressure is probably related to the positive volume of mixing observed in 1 atm glasses in this composition range. The enhanced solubility of SiO 2 in the TiO 2-rich liquid with pressure may be due to a pressure-induced increase in the coordination state of Si.

  17. Nanocrystals encapsulated in SiO2 particles: silanization and homogenous coating for bio applications.

    PubMed

    Yang, Ping; Li, Xiaoyu; Zhang, Ruili; Liu, Ning; Zhang, Yulan

    2013-03-01

    Sol-gel procedures have been developed to encapsulate inorganic nanocrystals including metallic Au and II-VI semiconductor materials (CdSe/Cd(1-x)Zn(x)S) in SiO2 particles by using tetraethyl orthosilicate. The key strategy was the control of a sol-gel procedure. The anisotropic deposition of SiO2 monomers occurs because well-developed crystal facets having different affinity to SiO2 monomers. SiO2 monomers were not homogeneously deposited on nonspherical Au and CdSe/Cd(1-x)Zn(x)S nanocrystals. A surface silanization process, partly hydrolyzed tetraethyl orthosilicate were attached to the nanocrystals instead of initial ligands, plays an important role for the nanocrystals coated homogeneously with a SiO2 layer. Furthermore, CdSe/Cd(1-x)Zn(x)S nanocrystals were homogeneously coated with a thin SiO2 layer by the surface silanization process and a subsequent reverse micelle route. Colloidal Au nanocrystals were homogeneously coated with a SiO2 shell by the surface silanization process and subsequent Stöber synthesis without using a silane coupling agent or bulk polymer as the surface primer to render the Au surface vitreophilic. These results indicated partly hydrolyzed tetraethyl orthosilicate has an ability to replace the ligand on nanocrystals. After surface modification, the SiO2 particles with nanocrystals were conjugated with antibody for bioapplications.

  18. Gap states in pentacene thin film induced by inert gas exposure.

    PubMed

    Bussolotti, Fabio; Kera, Satoshi; Kudo, Kazuhiro; Kahn, Antoine; Ueno, Nobuo

    2013-06-28

    We studied gas-exposure effects on pentacene (Pn) films on SiO2 and Au(111) substrates by ultrahigh sensitivity photoelectron spectroscopy, which can detect the density of states of ∼10(16) states eV-1 cm-3 comparable to electrical measurements. The results show the striking effects for Pn/SiO2: exposure to inert gas (N2 and Ar) produces a sharp rise in gap states from ∼10(16) to ∼10(18) states eV-1 cm-3 and pushes the Fermi level closer to the valence band (0.15-0.17 eV), as does exposure to O2 (0.20 eV), while no such gas-exposure effect is observed for Pn/Au(111). The results demonstrate that these gap states originate from small imperfections in the Pn packing structure, which are induced by gas penetration into the film through the crystal grain boundaries.

  19. Ultrahigh-pressure acoustic wave velocities of SiO2-Al2O3 glasses up to 200 GPa

    NASA Astrophysics Data System (ADS)

    Ohira, Itaru; Murakami, Motohiko; Kohara, Shinji; Ohara, Koji; Ohtani, Eiji

    2016-12-01

    Extensive experimental studies on the structure and density of silicate glasses as laboratory analogs of natural silicate melts have attempted to address the nature of dense silicate melts that may be present at the base of the mantle. Previous ultrahigh-pressure experiments, however, have been performed on simple systems such as SiO2 or MgSiO3, and experiments in more complex system have been conducted under relatively low-pressure conditions below 60 GPa. The effect of other metal cations on structural changes that occur in dense silicate glasses under ultrahigh pressures has been poorly understood. Here, we used a Brillouin scattering spectroscopic method up to pressures of 196.9 GPa to conduct in situ high-pressure acoustic wave velocity measurements of SiO2-Al2O3 glasses in order to understand the effect of Al2O3 on pressure-induced structural changes in the glasses as analogs of aluminosilicate melts. From 10 to 40 GPa, the transverse acoustic wave velocity ( V S ) of Al2O3-rich glass (SiO2 + 20.5 mol% Al2O3) was greater than that of Al2O3-poor glass (SiO2 + 3.9 mol% Al2O3). This result suggests that SiO2-Al2O3 glasses with higher proportions of Al ions with large oxygen coordination numbers (5 and 6) become elastically stiffer up to 40 GPa, depending on the Al2O3 content, but then soften above 40 GPa. At pressures from 40 to ~100 GPa, the increase in V S with increasing pressure became less steep than below 40 GPa. Above ~100 GPa, there were abrupt increases in the P-V S gradients ( dV S /dP) at 130 GPa in Al2O3-poor glass and at 116 GPa in Al2O3-rich glass. These changes resemble previous experimental results on SiO2 glass and MgSiO3 glass. Given that changes of dV S / dP have commonly been related to changes in the Si-O coordination states in the glasses, our results, therefore, may indicate a drastic structural transformation in SiO2-Al2O3 glasses above 116 GPa, possibly associated with an average Si-O coordination number change to higher than 6. Compared

  20. High-frequency magnetic permeability of single- and multilayered (Co41Fe39B20) x (SiO2)100- x nanocomposites

    NASA Astrophysics Data System (ADS)

    Tarasova, O. S.; Sitnikov, A. V.; Kalinin, Yu. E.; Starostenko, S. N.; Granovskii, A. B.

    2016-12-01

    Thin film single-layered (Co41Fe39B20) x (SiO2)100- x nanocomposites at x = 30-80 at % and multilayered nanocomposites composed of 176 pairs of [(Co41Fe39B20)60(SiO2)40]/[(Co41Fe39B20)60(SiO2)40 + O2] have been prepared via ion-beam sputtering of the complex target. The concentration dependences of the magnetic permeability of single-layered films at a frequency of 50 MHz are characterized by maximum losses near x = 60 at %, whereas the percolation threshold with respect to the electric conductivity is x = 50 at %. The high-frequency magnetic permeability of films has been measured by the resonator method in the frequency range of 0.1—10 GHz. As is shown, while the single-layer film passes to the multilayered structure, the ferromagnetic resonance frequency shifts from 1.5 to 2.5 GHz, and the imaginary part of the magnetic permeability attains 200 that is presumably due to the inhibition of the perpendicular magnetic anisotropy component.

  1. Stability and lattice dynamics of SiO2 cristobalite

    NASA Astrophysics Data System (ADS)

    Coh, Sinisa; Vanderbilt, David

    2008-03-01

    Among the phases of SiO2 are alpha and beta cristobalite. Despite early indications that the higher-temperature beta phase might be cubic (Fd3m), it is now accepted that it is in fact tetragonal (I42d), and that the experiments suggesting a cubic structure were averaging spatially or dynamically over tetragonal domains. Recently, Zhang and Scott (J. Phys. Cond.Matt. 19, 275201) suggested that the lower-temperature alpha phase, widely accepted to be tetragonal (P41212), might be an artifact in a similar way. With this motivation we investigate the energy landscape in the vicinity of cristobalite phases using first-principles calculations. We use the ABINIT implementation of density-functional theory in a plane-wave pseudopotential framework. We find that both the P41212 alpha and I42d beta phases are local minima, thus reinforcing that the identification of the alpha phase as belonging to the P41212 structure. We compute the frequencies of phonon modes at high-symmetry k-points in both structures and compare with experiment. We also identify a minimum-energy path connecting the alpha and beta phases through an intermediate orthorhombic phase (P212121), and find a surprisingly low barrier of ˜5,eV per formula unit. We note that a simple rigid-unit mode picture gives a good rough description of these energetics, and we map out the minimum-energy path in the space of rigid unit rotations in a physically insightful way.

  2. CdS nanoparticles incorporated onion-like mesoporous silica films: Ageing-induced large stokes shifted intense PL emission

    NASA Astrophysics Data System (ADS)

    Mishra, Manish Kr; Mandal, Abhijit; Saha, Jony; De, Goutam

    2013-10-01

    CdS nanoparticles (NPs) were generated in onion-like ordered mesoporous SiO2 films through a modified sol-gel process using P123 as a structure directing agent. Initially Cd2+ doped (12 equivalent mol% with respect to the SiO2) mesoporous SiO2 films were prepared on glass substrate. These films after heat-treatment at 350 °C in air yielded transparent mesoporous SiO2 films having hexagonally ordered onion-like pore channels embedded with uniformly dispersed CdO NPs. The generated CdO NPs were transformed into CdS NPs after exposing the films in H2S gas at 200 °C for 2 h. The as-prepared CdS NPs incorporated mesoporous SiO2 films (transparent and bright yellow in color) showed a band-edge emission at 485 nm and a weak surface defect related emission at 530 nm. During ageing of the films in ambient condition the band-edge emission gradually weakened with time and almost disappeared after about 15 days with concomitant increase of defect related strong surface state emission band near 615 nm. This transformation was related to the decay of initially formed well crystalline CdS to relatively smaller and weakly crystalline CdS NPs with surface defects due to gradual oxidation of surface sulfide. At this condition the embedded CdS NPs show large Stokes shifted (˜180 nm) intense broad emission which could be useful for luminescent solar concentrators. The detailed process was monitored by UV-Visible, FTIR and Raman spectroscopy, XPS, XRD and TEM studies. The evolution of photoluminescence (PL) and life times of CdS/SiO2 films were monitored with respect to the ageing time.

  3. Conformal SiO2 coating of sub-100 nm diameter channels of polycarbonate etched ion-track channels by atomic layer deposition.

    PubMed

    Sobel, Nicolas; Hess, Christian; Lukas, Manuela; Spende, Anne; Stühn, Bernd; Toimil-Molares, M E; Trautmann, Christina

    2015-01-01

    Polycarbonate etched ion-track membranes with about 30 µm long and 50 nm wide cylindrical channels were conformally coated with SiO2 by atomic layer deposition (ALD). The process was performed at 50 °C to avoid thermal damage to the polymer membrane. Analysis of the coated membranes by small angle X-ray scattering (SAXS) reveals a homogeneous, conformal layer of SiO2 in the channels at a deposition rate of 1.7-1.8 Å per ALD cycle. Characterization by infrared and X-ray photoelectron spectroscopy (XPS) confirms the stoichiometric composition of the SiO2 films. Detailed XPS analysis reveals that the mechanism of SiO2 formation is based on subsurface crystal growth. By dissolving the polymer, the silica nanotubes are released from the ion-track membrane. The thickness of the tube wall is well controlled by the ALD process. Because the track-etched channels exhibited diameters in the range of nanometres and lengths in the range of micrometres, cylindrical tubes with an aspect ratio as large as 3000 have been produced.

  4. The effects of a SiO2 coating on the corrosion parameters cpTi and Ti-6Al-7Nb alloy

    PubMed Central

    Basiaga, Marcin; Walke, Witold; Paszenda, Zbigniew; Karasiński, Paweł; Szewczenko, Janusz

    2014-01-01

    The aim of this paper was to evaluate the usefulness of the sol-gel method application, to modificate the surface of the Ti6Al7Nb alloy and the cpTi titanium (Grade 4) with SiO2 oxide, applied on the vascular implants to improve their hemocompatibility. Mechanical treatment was followed by film deposition on surface of the titanium samples. An appropriate selection of the process parameters was verified in the studies of corrosion, using potentiodynamic and impedance method. A test was conducted in the solution simulating blood vessels environment, in simulated body fluid at t = 37.0 ± 1 °C and pH = 7.0 ± 0.2. Results showed varied electrochemical properties of the SiO2 film, depending on its deposition parameters. Correlations between corrosion resistance and layer adhesion to the substrate were observed, depending on annealing temperature. PMID:25482412

  5. The effects of a SiO2 coating on the corrosion parameters cpTi and Ti-6Al-7Nb alloy.

    PubMed

    Basiaga, Marcin; Walke, Witold; Paszenda, Zbigniew; Karasiński, Paweł; Szewczenko, Janusz

    2014-01-01

    The aim of this paper was to evaluate the usefulness of the sol-gel method application, to modificate the surface of the Ti6Al7Nb alloy and the cpTi titanium (Grade 4) with SiO2 oxide, applied on the vascular implants to improve their hemocompatibility. Mechanical treatment was followed by film deposition on surface of the titanium samples. An appropriate selection of the process parameters was verified in the studies of corrosion, using potentiodynamic and impedance method. A test was conducted in the solution simulating blood vessels environment, in simulated body fluid at t = 37.0 ± 1 °C and pH = 7.0 ± 0.2. Results showed varied electrochemical properties of the SiO2 film, depending on its deposition parameters. Correlations between corrosion resistance and layer adhesion to the substrate were observed, depending on annealing temperature.

  6. Fabrication and properties of highly luminescent materials from Tb(OH)3@SiO2 and Tb(OH)3@SiO2:Eu3+ nanotubes

    NASA Astrophysics Data System (ADS)

    Thu Huong, Tran; Anh, Tran Kim; Minh, Le Quoc

    2009-09-01

    Luminescent nanomaterials with one-dimensional (1D) structures have attracted much attention due to their unique properties and potential applications in nanophotonics and nanobiophotonics. In this paper, we report a synthesis of terbium - hydroxide - at - silica Tb(OH)3@SiO2 and Tb(OH)3@SiO2:Eu3+ nanotubes. Terbium - hydroxide tubes were synthesized by soft template method. The size of the tubes can be controlled precisely and have outer diameters ranging from 80 to 120 nm, wall thickness of about 30 nm, and lengths ranging from 300 to 800 nm. To fabricate core/shell materials, the seed growth method is used. FESEM, X-ray diffraction, Raman spectra of Tb(OH)3 and Tb(OH)3@SiO2 nanotubes were investigated. The photoluminescence (PL) spectrum of Tb(OH)3 under 325 nm excitation consists of four main peaks at 488, 542, 582, and 618 nm. Furthermore, a preliminary suggestion for the mechanism of growth of the Tb(OH)3 nanotubes using the soft - template synthesis technique has been proposed. The PL intensity from Tb(OH)3@SiO2 or Tb(OH)3@SiO2:Eu3+ nanotubes is much stronger than that of Tb(OH)3.

  7. UV-Triggered Self-Healing of a Single Robust SiO2 Microcapsule Based on Cationic Polymerization for Potential Application in Aerospace Coatings.

    PubMed

    Guo, Wanchun; Jia, Yin; Tian, Kesong; Xu, Zhaopeng; Jiao, Jiao; Li, Ruifei; Wu, Yuehao; Cao, Ling; Wang, Haiyan

    2016-08-17

    UV-triggered self-healing of single microcapsules has been a good candidate to enhance the life of polymer-based aerospace coatings because of its rapid healing process and healing chemistry based on an accurate stoichiometric ratio. However, free radical photoinitiators used in single microcapsules commonly suffer from possible deactivation due to the presence of oxygen in the space environment. Moreover, entrapment of polymeric microcapsules into coatings often involves elevated temperature or a strong solvent, probably leading to swelling or degradation of polymer shell, and ultimately the loss of active healing species into the host matrix. We herein describe the first single robust SiO2 microcapsule self-healing system based on UV-triggered cationic polymerization for potential application in aerospace coatings. On the basis of the similarity of solubility parameters of the active healing species and the SiO2 precursor, the epoxy resin and cationic photoinitiator are successfully encapsulated into a single SiO2 microcapsule via a combined interfacial/in situ polymerization. The single SiO2 microcapsule shows solvent resistance and thermal stability, especially a strong resistance for thermal cycling in a simulated space environment. In addition, the up to 89% curing efficiency of the epoxy resin in 30 min, and the obvious filling of scratches in the epoxy matrix demonstrate the excellent UV-induced healing performance of SiO2 microcapsules, attributed to a high load of healing species within the capsule (up to 87 wt %) and healing chemistry based on an accurate stoichiometric ratio of the photoinitiator and epoxy resin at 9/100. More importantly, healing chemistry based on a UV-triggered cationic polymerization mechanism is not sensitive to oxygen, extremely facilitating future embedment of this single SiO2 microcapsule in spacecraft coatings to achieve self-healing in a space environment with abundant UV radiation and oxygen.

  8. Role of bovine serum albumin and humic acid in the interaction between SiO2 nanoparticles and model cell membranes.

    PubMed

    Wei, Xiaoran; Qu, Xiaolei; Ding, Lei; Hu, Jingtian; Jiang, Wei

    2016-12-01

    Silica nanoparticles (SiO2 NPs) can cause health hazard after their release into the environment. Adsorption of natural organic matter and biomolecules on SiO2 NPs alters their surface properties and cytotoxicity. In this study, SiO2 NPs were treated by bovine serum albumin (BSA) and humic acid (HA) to study their effects on the integrity and fluidity of model cell membranes. Giant and small unilamellar vesicles (GUVs and SUVs) were prepared as model cell membranes in order to avoid the interference of cellular activities. The microscopic observation revealed that the BSA/HA treated (BSA-/HA-) SiO2 NPs took more time to disrupt membrane than untreated-SiO2 NPs, because BSA/HA adsorption covered the surface SiOH/SiO(-) groups and weakened the interaction between NPs and phospholipids. The deposition of SiO2 NPs on membrane was monitored by a quartz crystal microbalance with dissipation (QCM-D). Untreated- and HA-SiO2 NPs quickly disrupted the SUV layer on QCM-D sensor; BSA-SiO2 NPs attached on the membranes but only caused slow vesicle disruption. Untreated-, BSA- and HA-SiO2 NPs all caused the gelation of the positively-charged membrane, which was evaluated by the generalized polarity values. HA-SiO2 NPs caused most serious gelation, and BSA-SiO2 NPs caused the least. Our results demonstrate that the protein adsorption on SiO2 NPs decreases the NP-induced membrane damage.

  9. Surface Acidity and Properties of TiO2/SiO2 Catalysts Prepared by Atomic Layer Deposition: UV-visible Diffuse Reflectance, DRIFTS, and Visible Raman Spectroscopy Studies

    DTIC Science & Technology

    2009-06-15

    the grafted TiO2 were in a highly dispersed amorphous form.19 Atomic layer deposition (ALD) is a thin film growth technique, which relies on self... Thin Films . U.S. Patent 4058430, 1977. (21) Ritala, M. Appl. Surf. Sci. 1997, 112, 223. TiO2 /SiO2 Catalysts Prepared by ALD J. Phys. Chem. C, Vol. 113...Surface Acidity and Properties of TiO2 /SiO2 Catalysts Prepared by Atomic Layer Deposition: UV-visible Diffuse Reflectance, DRIFTS, and Visible Raman

  10. Reduction of Mobile Pt Ion Density in SiO 2 and Si-SiO 2 Interface State Density in Pt-diffused Metal-Oxide-Semiconductor Structures

    NASA Astrophysics Data System (ADS)

    Deng, Bei; Shu, Chang; Kuwano, Hiroshi

    1995-07-01

    Platinum diffusion into bipolar devices introduces mobile Pt ions into SiO2 films and causes the state density at the Si-SiO2 interface to increase. Mobile Pt ions make the devices unstable and the increase in the interface state density causes enhancement of leakage current. MOS, metal-phosphosilicate glass-oxide-semiconductor (MGOS) and metal-silicon nitride-oxide-semiconductor (MNOS) structures are fabricated on (111) and (100) substrates in order to investigate means of reducing these adverse effects induced by Pt diffusion. Mobile Pt ions, the interface state density and the flat-band voltage for these structures are measured. The experimental results show that the MGOS structure with the (100) oriented substrate is most beneficial in reducing the adverse effects of Pt-diffused devices.

  11. Kinetics of valeric acid ketonization and ketenization in catalytic pyrolysis on nanosized SiO2, γ-Al2O3, CeO2/SiO2, Al2O3/SiO2 and TiO2/SiO2.

    PubMed

    Kulyk, Kostiantyn; Palianytsia, Borys; Alexander, John D; Azizova, Liana; Borysenko, Mykola; Kartel, Mykola; Larsson, Mats; Kulik, Tetiana

    2017-04-09

    Valeric acid is an important renewable platform chemical that can efficiently be produced from lignocellulosic biomass. Upgrading of valeric acid by catalytic pyrolysis has the potential to produce value added biofuels and chemicals on an industrial scale. Understanding the different mechanisms involved in the thermal transformations of valeric acid on the surface of nanosized oxides is important for the development of efficient heterogeneously-catalyzed pyrolytic conversion techniques. In this work, the thermal decomposition of valeric acid on the surface of nanoscale SiO2, γ-Al2O3, CeO2/SiO2, Al2O3/SiO2 and TiO2/SiO2 has been investigated by Temperature-Programmed Desorption Mass Spectrometry (TPD MS). Fourier transform infrared spectroscopy (FTIR) has been used to investigate the structure of valeric acid complexes on the oxide surfaces. Two main products of pyrolytic conversion were observed to be formed depending on the nano-catalyst used - dibutylketone and propylketene. The mechanisms of ketene and ketone formation from chemisorbed fragments of valeric acid are proposed and the kinetic parameters of the corresponding reactions were calculated. It was found that the activation energy of ketenization decreases in the order SiO2>γ-Al2O3>TiO2/SiO2>Al2O3/SiO2, and the activation energy of ketonization decreases in the order γ-Al2O3>CeO2/SiO2. Nano-oxide CeO2/SiO2 was found to selectively catalyze ketonization reaction.

  12. Nitridation of SiO2 for surface passivation

    NASA Technical Reports Server (NTRS)

    Lai, S. K. C.

    1985-01-01

    An attempt is made to relate the electrical properties of silicon dioxide film to the process history. A model is proposed to explain some of the observed results. It is shown that with our present knowledge of the dielectric, silicon dioxide film shows a lot of promise for its use in surface passivation, both for its resistance to impurity diffusion and for its resistance to radiation damage effects.

  13. Photoluminiscence response of Ru(II) complex immobilized in SiO2-based matrix to dissolved oxygen in beer.

    PubMed

    Anastasova, S; Milanova, M; Todorovsky, D

    2008-04-24

    The possibility to use the photoluminescence of Ru(II) tris(4,7-diphenyl-1,10-phenathroline) dichloride, immobilized in sol-gel produced SiO2-based matrix for the determination of dissolved oxygen concentration in beer is studied. Organically-modified silane (octyltriethoxysilane) and mixtures from tetraethoxysilane and octyltriethoxysilane are used as precursors for matrix production. Spin- and dip-coating techniques are applied for films deposition. The predeposition ultrasound treatment of the sol ensures a good sensitivity and a linear sensor quenching response to oxygen in 1/6 ppm O2-concentration interval. The CO2 present practically has no effect on the films performance. Their photoluminescence show rather good stability on prolonged storage in beer.

  14. Using Atom-Probe Tomography to Understand Zn O ∶Al /SiO 2/Si Schottky Diodes

    NASA Astrophysics Data System (ADS)

    Jaramillo, R.; Youssef, Amanda; Akey, Austin; Schoofs, Frank; Ramanathan, Shriram; Buonassisi, Tonio

    2016-09-01

    We use electronic transport and atom-probe tomography to study Zn O ∶Al /SiO 2/Si Schottky diodes on lightly doped n - and p -type Si. We vary the carrier concentration in the ZnO ∶Al films by 2 orders of magnitude, but the Schottky barrier height remains nearly constant. Atom-probe tomography shows that Al segregates to the interface, so that the ZnO ∶Al at the junction is likely to be metallic even when the bulk of the ZnO ∶Al film is semiconducting. We hypothesize that the observed Fermi-level pinning is connected to the insulator-metal transition in doped ZnO. This implies that tuning the band alignment at oxide/Si interfaces may be achieved by controlling the transition between localized and extended states in the oxide, thereby changing the orbital hybridization across the interface.

  15. High Temperature Aerogels in the Al2O3-SiO2 System

    NASA Technical Reports Server (NTRS)

    Hurwitz, Frances I.; Aranda, Denisse V.; Gallagher, Meghan E.

    2008-01-01

    Al2O3-SiO2 aerogels are of interest as constituents of thermal insulation systems for use at high temperatures. Al2O3 and mullite aerogels are expected to crystallize at higher temperatures than their SiO2 counterparts, hence avoiding the shrinkages that accompany the formation of lower temperature SiO2 phases and preserving pore structures into higher temperature regimes. The objective of this work is to determine the influence of processing parameters on shrinkage, gel structure (including surface area, pore size and distribution) and pyrolysis behavior.

  16. A Stable Monomeric SiO2 Complex with Donor-Acceptor Ligands.

    PubMed

    Rodriguez, Ricardo; Gau, David; Saouli, Jérémy; Baceiredo, Antoine; Saffon-Merceron, Nathalie; Branchadell, Vicenç; Kato, Tsuyoshi

    2017-03-27

    Isolation of a monomeric SiO2 compound 3 as a stable donor-acceptor complex with two different ligands -a σ-donating ligand (pyridine, dimethylaminopyridine, N-heterocyclic carbene) and a donor-acceptor ligand (iminophosphorane)-is presented. The SiO2 complex 3 is soluble in ordinary organic solvents and is stable at room temperature in solution and in the solid state. Of particular interest, 3 remains reactive and can be used as a stable and soluble unimolecular SiO2 reagent.

  17. Design of Al2O3/SiO2 laminated stacks with multiple interface dipole layers to achieve large flatband voltage shifts of MOS capacitors

    NASA Astrophysics Data System (ADS)

    Kamata, Hironobu; Kita, Koji

    2017-03-01

    We studied the dipole induced flatband voltage (VFB) shifts of Si MOS capacitors with Al2O3/SiO2/Al2O3/SiO2/Si laminated stacks ((Al2O3/SiO2)n/Si, n = 2) designed for a large positive shift of VFB. The VFB shift caused by each dipole layer was determined from capacitance-voltage characteristics by excluding the effect of fixed charges. Due to the additivity of multiple dipole layers in the laminated stack, a large VFB shift (>1 V) was observed. In our experimental condition, the dipole layers at Al2O3-on-SiO2 interfaces were selectively formed, while those at SiO2-on-Al2O3 interfaces were effectively suppressed. The validity of such additivity of VFB shifts induced by selectively formed dipole layers was also experimentally demonstrated for n ≥ 3 laminated stacks. An introduction of multiple dipole layers is applicable for a threshold voltage tuning in a wider range than the tuning with a single dipole layer.

  18. Synthesis for Magnetic Mesoporous Fe3O4-SiO2 Composites and Heterogeneous Fenton Degradation of Methyl Blue

    NASA Astrophysics Data System (ADS)

    Xie, Huanling; Zhang, Tengyun

    2014-12-01

    In this work, we presented a facile, one-step preparation for magnetic mesoporous Fe3O4-SiO2 composites under closely neutral conditions by an evaporation-induced self-assembly (EISA) and adding 1,3,5-TMB as co-solvent approach. The resulting samples were characterized by X-ray diffraction, N2 adsorption measurement, FT-IR and SEM. Magnetic mesoporous composites and H2O2 form heterogeneous Fenton in order to removal methylene blue as the dye wastewater model object. The catalysts showed high catalytic activity and stability in the decolorization of methlye blue.

  19. Insulin adsorption on crystalline SiO2: Comparison between polar and nonpolar surfaces using accelerated molecular-dynamics simulations

    NASA Astrophysics Data System (ADS)

    Nejad, Marjan A.; Mücksch, Christian; Urbassek, Herbert M.

    2017-02-01

    Adsorption of insulin on polar and nonpolar surfaces of crystalline SiO2 (cristobalite and α -quartz) is studied using molecular dynamics simulation. Acceleration techniques are used in order to sample adsorption phase space efficiently and to identify realistic adsorption conformations. We find major differences between the polar and nonpolar surfaces. Electrostatic interactions govern the adsorption on polar surfaces and can be described by the alignment of the protein dipole with the surface dipole; hence spreading of the protein on the surface is irrelevant. On nonpolar surfaces, on the other hand, van-der-Waals interaction dominates, inducing surface spreading of the protein.

  20. Passivation of Flexible YBCO Superconducting Current Lead With Amorphous SiO2 Layer

    NASA Technical Reports Server (NTRS)

    Johannes, Daniel; Webber, Robert

    2013-01-01

    across a thermal gradient with as little flow of heat as possible to make an efficient current lead. By protecting YBCO on a flexible substrate of low thermal conductivity with SiO2, a thermally efficient and flexible current lead can be fabricated. The technology is also applicable to current leads for 4 K superconducting electronics current biasing. A commercially available thin-film YBCO composite tape conductor is first stripped of its protective silver coating. It is then mounted on a jig that holds the sample flat and acts as a heat sink. Silicon dioxide is then deposited onto the YBCO to a thickness of about 1 micron using PECVD (plasma-enhanced chemical vapor deposition), without heating the YBCO to the point where degradation occurs. Since SiO2 can have good high-frequency electrical properties, it can be used to coat YBCO cable structures used to feed RF signals across temperature gradients. The prime embodiment concerns the conduction of DC current across the cryogenic temperature gradient. The coating is hard and electrically insulating, but flexible.

  1. EPR study of phenolic radical stabilization by grafting on SiO 2

    NASA Astrophysics Data System (ADS)

    Panagiota, Stathi; Louloudi, Maria; Deligiannakis, Yiannis

    2009-04-01

    A hybrid [SiO 2-GA] material has been synthesized by grafting Gallic acid (3,4,5-trihydroxybenzoic acid, GA) on SiO 2 via formation of amide bonds between amine groups on aminopropyl-silica and the carboxyl group of GA. The spatial fixation of GA prevents polymerization effects. EPR spectroscopy shows that GA radicals on [SiO 2-GA] show remarkable stability, comparable to that previously observed only for radicals in biological matrices on in soil organic matter. EPR reveals a bundle-like organization of the GA molecules on [SiO 2-GA] material. The relation of these factors to the enhanced radical stability is discussed.

  2. Broadband luminescence of Cu nanoparticles fabricated in SiO2 by ion implantation.

    PubMed

    Nguyen, Truong Khang; Le, Khai Q; Canimoglu, Adil; Can, Nurdogan

    2016-09-01

    In this study, we investigate optical properties of metal nanoparticle crystals fabricated by implanting copper (Cu) ions into single silica (SiO2) crystals with 400keV at various ion doses. The Cu implanted SiO2 (SiO2:Cu) crystal produces a broadband luminescence emission, ranging from blue to yellow, and having a blue luminescence peak at 546nm. Such anomalous luminescence emission bands suggest that the ion implantation may give rise to aggregation of Cu nanoparticles in the host matrix. The boundary element method-based modelling of a given Cu nanoparticle aggregation was employed to justify the broadband luminescence emission. Formation of Cu nanoparticles in SiO2 is predicted through their optical absorption data. The experimental results are compared with results of Mie calculations and we observe that the higher ion dose produces the larger particle size.

  3. QSAR model for cytotoxicity of SiO2 nanoparticles on human lung fibroblasts

    NASA Astrophysics Data System (ADS)

    Toropova, Alla P.; Toropov, Andrey A.; Benfenati, Emilio; Korenstein, Rafi

    2014-02-01

    The possibility of building up predictive model for cytotoxicity of SiO2-nanoparticles (SiO2-NPs) by means of so-called optimal descriptors which are mathematical functions of size and concentration of SiO2-NPs is demonstrated with data on sixteen systems' "size-concentration." The calculation has been carried out by means of the CORAL software (http://www.insilico.eu/coral/). The statistical quality of the best model for the cytotoxic inhibition ratio (%) of human lung fibroblasts cultured in the media containing different concentrations of SiO2-NPs which is measured by MTT assay is the following: n = 10, r 2 = 0.9837, s = 2.53 %, F = 483 (training set) and n = 6, r 2 = 0.9269, s = 7.94 % (test set). The perspectives of this approach are discussed.

  4. Properties of Cathodoluminescence for Cryogenic Applications of SiO2-based Space Observatory Optics and Coatings

    NASA Technical Reports Server (NTRS)

    Evans, Amberly; Dennison, J.R.; Wilson, Gregory; Dekany, Justin; Bowers Charles W.; Meloy, Robert; Heaney, James B.

    2013-01-01

    Disordered thin film SiO2SiOx coatings undergoing electron-beam bombardment exhibit cathodoluminescence, which can produce deleterious stray background light in cryogenic space-based astronomical observatories exposed to high-energy electron fluxes from space plasmas. As future observatory missions push the envelope into more extreme environments and more complex and sensitive detection, a fundamental understanding of the dependencies of this cathodoluminescence becomes critical to meet performance objectives of these advanced space-based observatories. Measurements of absolute radiance and emission spectra as functions of incident electron energy, flux, and power typical of space environments are presented for thin (60-200 nm) SiO2SiOx optical coatings on reflective metal substrates over a range of sample temperatures (40-400 K) and emission wavelengths (260-5000 nm). Luminescent intensity and peak wavelengths of four distinct bands were observed in UVVISNIR emission spectra, ranging from 300 nm to 1000 nm. A simple model is proposed that describes the dependence of cathodoluminescence on irradiation time, incident flux and energy, sample thickness, and temperature.

  5. Optimization of SiO2-TiNxOy-Cu interference absorbers: numerical and experimental results

    NASA Astrophysics Data System (ADS)

    Lazarov, Michel P.; Sizmann, R.; Frei, Ulrich

    1993-10-01

    SiO2 - TiNxOy-Cu absorbers were prepared with activated reactive evaporation (ARE). The deposition parameters for the ARE process were adjusted according to the results of the numerical optimizations by a genetic algorithm. We present spectral reflectance, calorimetric and grazing incidence X-ray reflection (GXR) measurements. Best coatings for applications as selective absorber in the range of T equals 100 (DOT)(DOT)(DOT) 200 degree(s)C exhibit a solar absorptance of 0.94 and a near normal emittance of 0.044 at 100 degree(s)C. This emittance is correlated with the hemispherical emittance of 0.061 obtained from calorimetric measurements at 200 degree(s)C. First results on lifetime studies show that the coatings are thermally stable under vacuum up to 400 degree(s)C. The SiO2 film passivates the absorber, a substantial slow down of degradation in dry air is observed. Our tests demonstrate that the coating will withstand break down in cooling fluid and vacuum if mounted in an evacuated collector.

  6. Facile approach in fabricating superhydrophobic SiO2/polymer nanocomposite coating

    NASA Astrophysics Data System (ADS)

    Chen, Hengzhen; Zhang, Xia; Zhang, Pingyu; Zhang, Zhijun

    2012-11-01

    We have developed a facile spin-coating method to prepare water-repellent SiO2/polymer composite coating without any surface chemical modification. The wettability can be adjusted by controlling the content of SiO2 nanoparticles. The coating demonstrates sustainable superhydrophobicity in the condition of continuous contact with corrosive liquids. Importantly, the coating can be fabricated on various metal substrates to prevent metal from corrosion.

  7. Effect of helium on structure and compression behavior of SiO2 glass

    PubMed Central

    Shen, Guoyin; Mei, Qiang; Prakapenka, Vitali B.; Lazor, Peter; Sinogeikin, Stanislav; Meng, Yue; Park, Changyong

    2011-01-01

    The behavior of volatiles is crucial for understanding the evolution of the Earth’s interior, hydrosphere, and atmosphere. Noble gases as neutral species can serve as probes and be used for examining gas solubility in silicate melts and structural responses to any gas inclusion. Here, we report experimental results that reveal a strong effect of helium on the intermediate range structural order of SiO2 glass and an unusually rigid behavior of the glass. The structure factor data show that the first sharp diffraction peak position of SiO2 glass in helium medium remains essentially the same under pressures up to 18.6 GPa, suggesting that helium may have entered in the voids in SiO2 glass under pressure. The dissolved helium makes the SiO2 glass much less compressible at high pressures. GeO2 glass and SiO2 glass with H2 as pressure medium do not display this effect. These observations suggest that the effect of helium on the structure and compression of SiO2 glass is unique. PMID:21444785

  8. Photoluminescence properties of hybrid SiO2-coated CdTe/CdSe quantum dots.

    PubMed

    Liu, Ning; Yang, Ping

    2014-09-01

    Hybrid SiO2-coated CdTe/CdSe quantum dots (QDs) were prepared using CdTe/CdSe QDs prepared by hydrothermal synthesis. A CdSe interlayer made CdTe/CdSe cores with unique type II heterostructures. The hybrid SiO2-coated CdTe/CdSe QDs revealed excellent photoluminescence (PL) properties compared with hybrid SiO2-coated CdTe QDs. Because of the existence of spatial separations of carriers in the type II CdTe/CdSe core/shell QDs, the hybrid QDs had a relatively extended PL lifetime and high stability in phosphate-buffered saline buffer solutions. This is ascribed to the unique components and stable surface state of hybrid SiO2-coated CdTe/CdSe QDs. During the stabilization test in phosphate-buffered saline buffer solutions, both static and dynamic quenching occurred. The quenching mechanism of the hybrid QDs was not suited with the Stern–Volmer equation. However, the relative stable surface of CdTe/CdSe QDs resulted in lower degradation and relative high PL quantum yields compared with hybrid SiO2-coated CdTe QDs. As a result, hybrid SiO2-coated CdTe/CdSe QDs can be used in bioapplications.

  9. Self-cleaning and superhydrophilic wool by TiO2/SiO2 nanocomposite

    NASA Astrophysics Data System (ADS)

    Pakdel, Esfandiar; Daoud, Walid A.; Wang, Xungai

    2013-06-01

    Wool fabrics were functionalised using TiO2 and TiO2/SiO2 nanocomposites through a low-temperature sol-gel method. Titanium terta isopropoxide (TTIP) and tetra ethylorthosilicate (TEOS) were employed as precursors of TiO2 and SiO2, respectively. Nanocomposite sols were devised based on three molar ratio percentages of TiO2/SiO2 70:30, 50:50, and 30:70 to investigate the role of each component. The self-cleaning and hydrophilicity of wool fabrics were analysed based on the removal of coffee stain under UV and water droplet contact angle measurements, respectively. It was observed that applying TiO2/SiO2 50:50 and 30:70 sols to wool rendered the fabric superhydrophilic. Fabrics functionalised with TiO2/SiO2 30:70 showed the highest efficiency in stain removal, followed by samples functionalised with TiO2/SiO2 50:50.

  10. Space Weathering of Silicates Simulated by Successive Laser Irradiation: In Situ Reflectance Measurements of Fo90, Fo99+, and Sio2

    NASA Technical Reports Server (NTRS)

    Loeffler, M. J.; Dukes, C. A.; Christoffersen, R.; Baragiola, R. A.

    2016-01-01

    Pulsed-laser irradiation causes the visible-near-infrared spectral slope of olivine (Fo90 and Fo99+) and SiO2 to increase (redden), while the olivine samples darken and the SiO2 samples brighten slightly. XPS analysis shows that irradiation of Fo90 produces metallic Fe. Analytical SEM and TEM measurements confirm that reddening in the Fo90 olivine samples correlates with the production of nanophase metallic Fe (npFe0) grains, 2050 nm in size. The reddening observed in the SiO2 sample is consistent with the formation of SiO or other SiOx species that absorb in the visible. The weak spectral brightening induced by laser irradiation of SiO2 is consistent with a change in surface topography of the sample. The darkening observed in the olivine samples is likely caused by the formation of larger npFe0 particles, such as the 100400 nm diameter npFe0 identified during our TEM analysis of Fo90 samples. The Fo90 reflectance spectra are qualitatively similar to those in previous experiments suggesting that in all cases formation of npFe0 is causing the spectral alteration. Finally, we find that the accumulation of successive laserpulses cause continued sample darkening in the Vis-NIR, which suggests that repeated surface impacts are an efficient way to darken airless body surfaces.

  11. Space Weathering of Silicates Simulated by Successive Laser Irradiation: in Situ Reflectance Measurements of Fo90, Fo99+, and SiO2

    NASA Technical Reports Server (NTRS)

    Loeffler, M. J.; Dukes, C. A.; Christoffersen, R.; Baragiola, R. A.

    2016-01-01

    Pulsed-laser irradiation causes the visible-near-infrared spectral slope of olivine (Fo90 and Fo99+) and SiO2 to increase (redden), while the olivine samples darken and the SiO2 samples brighten slightly. XPS analysis shows that irradiation of Fo90 produces metallic Fe. Analytical SEM and TEM measurements confirm that reddening in the Fo90 olivine samples correlates with the production of "nanophase" metallic Fe (npFe0) grains, 20-50 nm in size. The reddening observed in the SiO2 sample is consistent with the formation of SiO or other SiOx species that absorb in the visible. The weak spectral brightening induced by laser irradiation of SiO2 is consistent with a change in surface topography of the sample. The darkening observed in the olivine samples is likely caused by the formation of larger npFe0 particles, such as the 100-400 nm diameter npFe0 identified during our TEM analysis of Fo90 samples. The Fo90 reflectance spectra are qualitatively similar to those in previous experiments suggesting that in all cases formation of npFe0 is causing the spectral alteration. Finally, we find that the accumulation of successive laser pulses cause continued sample darkening in the Vis-NIR, which suggests that repeated surface impacts are an efficient way to darken airless body surfaces.

  12. Space weathering of silicates simulated by successive laser irradiation: In situ reflectance measurements of Fo90, Fo99+, and SiO2

    NASA Astrophysics Data System (ADS)

    Loeffler, M. J.; Dukes, C. A.; Christoffersen, R.; Baragiola, R. A.

    2016-02-01

    Pulsed-laser irradiation causes the visible-near-infrared spectral slope of olivine (Fo90 and Fo99+) and SiO2 to increase (redden), while the olivine samples darken and the SiO2 samples brighten slightly. XPS analysis shows that irradiation of Fo90 produces metallic Fe. Analytical SEM and TEM measurements confirm that reddening in the Fo90 olivine samples correlates with the production of "nanophase" metallic Fe (npFe0) grains, 20-50 nm in size. The reddening observed in the SiO2 sample is consistent with the formation of SiO or other SiOx species that absorb in the visible. The weak spectral brightening induced by laser irradiation of SiO2 is consistent with a change in surface topography of the sample. The darkening observed in the olivine samples is likely caused by the formation of larger npFe0 particles, such as the 100-400 nm diameter npFe0 identified during our TEM analysis of Fo90 samples. The Fo90 reflectance spectra are qualitatively similar to those in previous experiments suggesting that in all cases formation of npFe0 is causing the spectral alteration. Finally, we find that the accumulation of successive laser pulses cause continued sample darkening in the Vis-NIR, which suggests that repeated surface impacts are an efficient way to darken airless body surfaces.

  13. Highly active surface-enhanced Raman scattering (SERS) substrates based on gold nanoparticles infiltrated into SiO2 inverse opals

    NASA Astrophysics Data System (ADS)

    Ankudze, Bright; Philip, Anish; Pakkanen, Tuula T.; Matikainen, Antti; Vahimaa, Pasi

    2016-11-01

    SiO2 inverse opal (IO) films with embedded gold nanoparticles (AuNPs) for surface-enhanced Raman scattering (SERS) application are reported. SiO2 IO films were loaded with AuNPs by a simple infiltration in a single cycle to form Au-SiO2 IOs. The optical property and the morphology of the Au-SiO2 IO substrates were characterized; it was observed that they retained the Bragg diffraction of SiO2 IO and the localized surface plasmon resonance (LSPR) of AuNPs. The SERS property of the Au-SiO2 IO substrates were studied with methylene blue (MB) and 4-aminothiophenol (4-ATP). The SERS enhancement factors were 107 and 106 for 4-ATP and MB, respectively. A low detection limit of 10-10 M for 4-ATP was also obtained with the Au-SiO2 IO substrate. A relative standard deviation of 18.5% for the Raman signals intensity at 1077 cm-1 for 4-ATP shows that the Au-SiO2 IO substrates have good signal reproducibility. The results of this study indicate that the Au-SiO2 IO substrates can be used in sensing and SERS applications.

  14. Induced changes in refractive index, optical band gap, and absorption edge of polycarbonate-SiO2 thin films by Vis-IR lasers

    NASA Astrophysics Data System (ADS)

    Ehsani, Hassan; Akhoondi, Somaieh

    2016-09-01

    In this experimental work, we have studied induced changes in refractive index, extinction coefficient, and optical band-gap of Bisphenol-A-polycarbonate (BPA-PC) coated with a uniform and thin, anti-scratch SiO2 film irradiated by visible to near-infrared lasers at 532 nm (green),650 nm(red), and 980 nm (IR)wavelength lasers with different energy densities. Our lasers sources are indium-gallium-aluminum-phosphide, second harmonic of neodymium-YAG-solid state lasers and gallium-aluminum-arsenide-semiconductor laser. The energy densities of our sources have been changed by changing the spot size of incident laser. samples transmission spectra were monitored by carry500 spectrophotometer and induced changes in optical properties are evaluated by using, extrapolation of the transmission spectrum through Swanepoel method and computer application

  15. Direct growth of doping-density-controlled hexagonal graphene on SiO2 substrate by rapid-heating plasma CVD.

    PubMed

    Kato, Toshiaki; Hatakeyama, Rikizo

    2012-10-23

    A transfer-free method for growing carrier-density-controlled graphene directly on a SiO(2) substrate has been realized for the first time by rapid-heating plasma chemical vapor deposition (RH-PCVD). Using this method, high-quality single-layer graphene sheets with a hexagonal domain can be selectively grown between a Ni film and a SiO(2) substrate. Systematic investigations reveal that the relatively thin Ni layer, rapid heating, and plasma CVD are critical to the success of this unique method of graphene growth. By applying this technique, an easy and scalable graphene-based field effect transistor (FET) fabrication is also demonstrated. The electrical transport type of the graphene-based FET can be precisely tuned by adjusting the NH(3) gas concentration during the RH-PCVD process.

  16. Raspberrylike SiO2@reduced graphene oxide@AgNP composite microspheres with high aqueous dispersity and excellent catalytic activity.

    PubMed

    Xiao, Wei; Zhang, Yanhua; Liu, Bitao

    2015-03-25

    The hybridizations of functional microspheres with graphene or graphene oxide (GO) sheets often suffer from severe agglomeration behaviors, leading to poor water dispersity of the resultant composite materials. Here, we first demonstrate that the sonication-assisted self-assembly of tiny GO sheets (whose lateral size less than 200 nm) on microspheric substrates like cationic polyelectrolyte-modified SiO2 microspheres could effectively overcome such a common drawback. On the basis of this facile strategy, we further developed reduced graphene oxide/silver nanoparticle composite film wrapped SiO2 microspheres, which not only possessed unique raspberrylike structure and high aqueous dispersity but also exhibited exceptional catalytic activity toward the reduction of 4-nitrophenol.

  17. A 1550 nm PbS semiconductor quantum dots fiber amplifier based on SiO2 sol-gel method

    NASA Astrophysics Data System (ADS)

    Sun, Xiaolan; Li, Chao; Xie, Libin; Liu, Xiaohong; Dong, Yanhua

    2011-12-01

    A novel PbS quantum dots (QDs) fiber amplifier based on SiO2 Sol-Gel method was proposed. The QDs doped SiO2 films was deposited onto a fused tapered fiber coupler based on standard single mode fiber (SMF). With a 980 nm wavelength laser diode (LD) as the pump, 1550 nm signal and 980 nm pump light waves were injected into the tapered region simultaneously, through the evanescent wave, we obtained the gain at 1576 nm wavelength as high as 5 dB. The proposed fiber amplififier can implement the property of a small, integrated, high output, low noise, high gain, low cost, which meet the need of the future of optical fiber communication system.

  18. Fabrication of ZIF-8@SiO2 Micro/Nano Hierarchical Superhydrophobic Surface on AZ31 Magnesium Alloy with Impressive Corrosion Resistance and Abrasion Resistance.

    PubMed

    Wu, Cuiqing; Liu, Qi; Chen, Rongrong; Liu, Jingyuan; Zhang, Hongsen; Li, Rumin; Takahashi, Kazunobu; Liu, Peili; Wang, Jun

    2017-03-29

    Superhydrophobic coatings are highly promising for protecting material surfaces and for wide applications. In this study, superhydrophobic composites, comprising a rhombic-dodecahedral zeolitic imidazolate framework (ZIF-8@SiO2), have been manufactured onto AZ31 magnesium alloy via chemical etching and dip-coating methods to enhance stability and corrosion resistance. Herein, we report on a simple strategy to modify hydrophobic hexadecyltrimethoxysilan (HDTMS) on ZIF-8@SiO2 to significantly improve the property of repelling water. We show that various liquids can be stable on its surface and maintain a contact angle higher than 150°. The morphologies and chemical composition were characterized by means of scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FI-IR). In addition, the anticorrosion and antiattrition properties of the film were assessed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization and HT, respectively. Such a coating shows promising potential as a material for large-scale fabrication.

  19. Influence of in situ applied ultrasound during Si+ implantation in SiO2 on paramagnetic defect generation

    NASA Astrophysics Data System (ADS)

    Jivanescu, M.; Romanyuk, A.; Stesmans, A.

    2010-06-01

    Electron spin resonance (ESR) results are presented on the influence of in situ ultrasound treatment (UST) during implantation at 300 K of Si+ ions into thermal SiO2 on (100)Si before and after subsequent high-temperature (T) annealing (1100 °C) intended to promote the formation of embedded Si nanoparticles. The as-implanted state exhibits high densities of three prominent types of point defects, including the SiO2-specific S and E'γ O-vacancy type centers, and an unknown broad (≈20 G) signal at g≈2.0026 denoted IS. The high-intensity S signal shows demagnetization shape effects, pointing to a distribution of high local density of defects over a thin layer. UST is observed to effectuate a drastic reduction in S and E'γ centers, and elimination of IS beyond detection. This reveals a strong healing influence of in situ transferred ultrasound (US) energy on implantation-induced damage, here quantified and identified on atomic level in terms of mainly intrinsic paramagnetic point defects elimination, viz., Frenkel pair elimination, while all three initial signals disappear. Other types of defects surface after annealing of the non-US treated sample, including the SiO2-specific EX defect signal and Pb-type Si/SiO2 interface centers, the appearance of the latter providing direct ESR evidence for crystallization of the excess Si nanoparticles. The influence of the UST healing effect is kept up after subsequent annealing, now resulting in the absence of virtually all ESR-active centers. The drop in Pb-type centers below the detection level in the UST annealed sample indicates improvement of the nanocrystalline-Si/SiO2 interface quality. The combination of UST with high-T annealing emerges as a highly efficient means to eradicate ion implantation damage in terms of intrinsic point defects.

  20. Fabrication of biomimetic high performance antireflective and antifogging film by spin-coating.

    PubMed

    Zhang, Liang; Lü, Changli; Li, Yunfeng; Lin, Zhe; Wang, Zhanhua; Dong, Heping; Wang, Tieqiang; Zhang, Xuemin; Li, Xiao; Zhang, Junhu; Yang, Bai

    2012-05-15

    In this paper, we report a facile way to fabricate biomimetic high performance optical hybrid films with excellent antireflective and antifogging properties by one-step spin-coating the mixture of mesoporous SiO(2) particles and SiO(2) sol. The production process of the films is easy, low-cost, and time-efficient. Mesoporous SiO(2) particles containing surfactants disperse in SiO(2) sol stably without any chemical modification, which decrease the effective refractive index and increase the transmittance of the films. In addition, such films possess superhydrophilic properties and exhibit high performance antifogging properties. Due to the good film forming performance of SiO(2) sol, mesoporous SiO(2) particles are embedded in the films and impart the films high mechanical stability and durability. The surface morphology of the films can maintain well after repeated friction, and the performances of antireflective and antifogging also do not change as well.

  1. Relationship between lymphocyte DNA fragmentation and dose of iron oxide (Fe2O3) and silicon oxide (SiO2) nanoparticles.

    PubMed

    Jiménez-Villarreal, J; Rivas-Armendáriz, D I; Arellano Pérez-Vertti, R D; Olivas Calderón, E; García-Garza, R; Betancourt-Martínez, N D; Serrano-Gallardo, L B; Morán-Martínez, J

    2017-02-08

    At present, the use of nanoparticles is a controversial topic, especially when analyzing their effects in human tissues. Nanoparticles (NPs) can cause oxidative stress by increasing membrane lipids peroxidation and reactive oxygen species, and decreasing intracellular glutathione. Oxidative stress plays an important role in cell signaling and inflammatory responses. It can result in genotoxicity, affect cell proliferation, and induce DNA damage. The objective of this study is to evaluate the genotoxic potential of NPs in lymphocyte DNA. Wistar female rats (N = 45) were sorted in three randomized groups as follows: Group 1 (N = 20); Group 2 (N = 20) and a control group (N = 5). A single dose of iron oxide (Fe2O3) and silicon oxide (SiO2) NPs dissolved in saline solution were administered orally to the rats. Cardiac puncture was performed to extract peripheral blood for genotoxic analysis. DNA fragmentation for lymphocytes was performed. Control rats showed a fragmentation percentage of 11.20 ± 2.16%. Rats exposed to SiO2 and Fe2O3 NPs for 24 h showed statistically significant differences in DNA fragmentation percentages as compared with that of the control group. A lineal dose-response correlation between genotoxic damage and exposure to SiO2 and Fe2O3 NPs was found (r(2) = 0.99 and 0.98 for SiO2 and Fe2O3, respectively). In conclusion, we found that exposure to Fe2O3 and SiO2 NPs can cause DNA fragmentation in lymphocytes in a dose-dependent manner.

  2. Structural color in porous, superhydrophilic, and self-cleaning SiO2/TiO2 Bragg stacks.

    PubMed

    Wu, Zhizhong; Lee, Daeyeon; Rubner, Michael F; Cohen, Robert E

    2007-08-01

    Thin-film Bragg stacks exhibiting structural color have been fabricated by a layer-by-layer (LbL) deposition process involving the sequential adsorption of nanoparticles and polymers. High- and low-refractive-index regions of quarter-wave stacks were generated by calcining LbL-assembled multilayers containing TiO(2) and SiO(2) nanoparticles, respectively. The physical attributes of each region were characterized by a recently developed ellipsometric method. The structural color characteristics of the resultant nanoporous Bragg stacks could be precisely tuned in the visible region by varying the number of stacks and the thickness of the high- and low-refractive-index stacks. These Bragg stacks also exhibited potentially useful superhydrophilicity and self-cleaning properties.

  3. TEM studies of Ge nanocrystal formation in PECVD grown SiO2:Ge/SiO2 multilayers

    NASA Astrophysics Data System (ADS)

    Agan, S.; Dana, A.; Aydinli, A.

    2006-06-01

    We investigate the effect of annealing on the Ge nanocrystal formation in multilayered germanosilicate-oxide films grown on Si substrates by plasma enhanced chemical vapour deposition (PECVD). The multilayered samples were annealed at temperatures ranging from 750 to 900 °C for 5 min under nitrogen atmosphere. The onset of formation of Ge nanocrystals, at 750 °C, can be observed via high resolution TEM micrographs. The diameters of Ge nanocrystals were observed to be between 5 and 14 nm. As the annealing temperature is raised to 850 °C, a second layer of Ge nanocrystals forms next to the original precipitation band, positioning itself closer to the substrate SiO2 interface. High resolution cross section TEM images, electron diffraction and electron energy-loss spectroscopy as well as energy-dispersive x-ray analysis (EDAX) data all indicate that Ge nanocrystals are present in each layer.

  4. Exploring Pd adsorption, diffusion, permeation, and nucleation on bilayer SiO2/Ru as a function of hydroxylation and precursor environment: From UHV to catalyst preparation

    NASA Astrophysics Data System (ADS)

    Pomp, Sascha; Kaden, William E.; Sterrer, Martin; Freund, Hans-Joachim

    2016-10-01

    The hydroxylation-dependent permeability of bilayer SiO2 supported on Ru(0001) was investigated by XPS and TDS studies in a temperature range of 100 K to 600 K. For this, the thermal behavior of Pd evaporated at 100 K, which results in surface and sub-surface (Ru-supported) binding arrangements, was examined relative to the extent of pre-hydroxylation. Samples containing only defect-mediated hydroxyls showed no effect on Pd diffusion through the film at low temperature. If, instead, the concentration of strongly bound hydroxyl groups and associated weakly bound water molecules was enriched by an electron-assisted hydroxylation procedure, the probability for Pd diffusion through the film is decreased via a pore-blocking mechanism. Above room temperature, all samples showed similar behavior, reflective of particle nucleation above the film and eventual agglomeration with any metal atoms initially binding beneath the film. When depositing Pd onto the same SiO2/Ru model support via adsorption of [Pd(NH3)4]Cl2 from alkaline (pH 12) precursor solution, we observe notably different adsorption and nucleation mechanisms. The resultant Pd adsorption complexes follow established decomposition pathways to produce model catalyst systems compatible with those created exclusively within UHV despite lacking the ability to penetrate the film due to the increased size of the initial Pd precursor groups.

  5. Memory and learning behaviors mimicked in nanogranular SiO2-based proton conductor gated oxide-based synaptic transistors

    NASA Astrophysics Data System (ADS)

    Wan, Chang Jin; Zhu, Li Qiang; Zhou, Ju Mei; Shi, Yi; Wan, Qing

    2013-10-01

    In neuroscience, signal processing, memory and learning function are established in the brain by modifying ionic fluxes in neurons and synapses. Emulation of memory and learning behaviors of biological systems by nanoscale ionic/electronic devices is highly desirable for building neuromorphic systems or even artificial neural networks. Here, novel artificial synapses based on junctionless oxide-based protonic/electronic hybrid transistors gated by nanogranular phosphorus-doped SiO2-based proton-conducting films are fabricated on glass substrates by a room-temperature process. Short-term memory (STM) and long-term memory (LTM) are mimicked by tuning the pulse gate voltage amplitude. The LTM process in such an artificial synapse is due to the proton-related interfacial electrochemical reaction. Our results are highly desirable for building future neuromorphic systems or even artificial networks via electronic elements.In neuroscience, signal processing, memory and learning function are established in the brain by modifying ionic fluxes in neurons and synapses. Emulation of memory and learning behaviors of biological systems by nanoscale ionic/electronic devices is highly desirable for building neuromorphic systems or even artificial neural networks. Here, novel artificial synapses based on junctionless oxide-based protonic/electronic hybrid transistors gated by nanogranular phosphorus-doped SiO2-based proton-conducting films are fabricated on glass substrates by a room-temperature process. Short-term memory (STM) and long-term memory (LTM) are mimicked by tuning the pulse gate voltage amplitude. The LTM process in such an artificial synapse is due to the proton-related interfacial electrochemical reaction. Our results are highly desirable for building future neuromorphic systems or even artificial networks via electronic elements. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr02987e

  6. Relaxation Properties of Single Layer Graphene on SiO2 Substrate.

    PubMed

    Wang, Weidong; Li, Shuai; Min, Jiaojiao; Shen, Cuili

    2015-04-01

    The relaxation properties of single layer graphene sheet on the SiO2 substrate are investigated through molecular dynamics simulation technique in this article. The graphene sheet models with different aspect ratios on SiO2 substrate are established and sufficiently relaxed at different thermodynamic temperatures. Subsequently, the morphology, equilibrium position and undulation of graphene on SiO2 substrate are discussed. It is observed that after sufficient relaxation processes, all the graphene sheets are adsorbed on SiO2 substrates and have some certain degree of undulations both on the edge and in the inner surface rather than perfect planar structures. Further observation from the simulation results shows that with different initial distances between the graphene sheet and SiO2 substrate, the graphene sheet would eventually stabilize to an identical equilibrium level at the same temperature. In addition, the final average distance between the graphene sheet and the substrate is a constant of 3.44 A at 0.01 K, in close proximity to the value of parameter r in Lennard-Jones potential function, and the higher the temperature is, the larger the final distance becomes. The results also indicate that for the same size of the graphene sheet, the increasing of temperature significantly aggravates the undulation of graphene sheet. With the increase of aspect ratios, the undulation of the graphene sheet is also aggravated, even the graphene sheet would crimp to a certain extent.

  7. Tribological properties and lubricating mechanism of SiO2 nanoparticles in water-based fluid

    NASA Astrophysics Data System (ADS)

    Bao, Y. Y.; Sun, J. L.; Kong, L. H.

    2017-03-01

    The tribological properties of surface modified SiO2 nanoparticles suspension in water-based lubricant have been studied. SiO2 (30 nm) nanoparticles were dispersed through surface modification with polyethylene glycol-200. Transmission electron microscope (TEM) and infrared (IR) spectroscopy show that SiO2 nanoparticles disperse well and stably in the water-based lubricant. The diameter of the nanoparticles is about 60 nm. Tribological properties of the water-based lubricant were evaluated using four-ball wear test machine and pin-on-disk tester under different loads and different concentrations of SiO2 nanoparticles. Wear surface morphology, element chemistry configuration of steel balls and steel rings were studied by means of X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Results show that the tribological properties of the water-based fluid have been improved by addition of nanoparticles ranging from 0.1% to 0.3% concentrations. SiO2 nanoparticles deposited onto the wear surface during the sliding, which helped to reduce the friction coefficients and increase the anti-wear properties due to the miniature ball bearing effect and self-repairing performance of nanoparticles between the friction pairs. With the increase of test load, the friction coefficients decrease but the wear of the surface increase.

  8. Development of nano SiO2 incorporated nano zinc phosphate coatings on mild steel

    NASA Astrophysics Data System (ADS)

    Tamilselvi, M.; Kamaraj, P.; Arthanareeswari, M.; Devikala, S.; Selvi, J. Arockia

    2015-03-01

    This paper reports the development of nano SiO2 incorporated nano zinc phosphate coatings on mild steel at low temperature for achieving better corrosion protection. A new formulation of phosphating bath at low temperature with nano SiO2 was attempted to explore the possibilities of development of nano zinc phosphate coatings on mild steel with improved corrosion resistance. The coatings developed were studied by Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDX), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Electrochemical measurements. Significant variation in the coating weight, morphology and corrosion resistance was observed as nano SiO2 concentrations varied from 0.5-4 g/L. The results showed that, the nano SiO2 in the phosphating solution changed the initial potential of the interface between mild steel substrate and phosphating solution and reduce the activation energy of the phosphating process, increase the nucleation sites and yielded zinc phosphate coatings of higher coating weight, greater surface coverage and enhanced corrosion resistance. Better corrosion resistance was observed for coatings derived from phosphating bath containing 1.5 g/L nano SiO2. The new formulation reported in the present study was free from Ni or Mn salts and had very low concentration of sodium nitrite (0.4 g/L) as accelerator.

  9. Superamphiphobic surfaces constructed by cross-linked hollow SiO2 spheres

    NASA Astrophysics Data System (ADS)

    Cui, Weihao; Wang, Tao; Yan, Aili; Wang, Sheng

    2017-04-01

    By using stringed carbon spheres as template material, a series of hierarchical 3D cross-linked SiO2 coated carbon spheres and hollow SiO2 spheres were fabricated, and spray-coated on glass slides, followed by the fluorination treatment with per-fluorotrichlorosilane. The surface characterization and surface wettability data indicated that hollow SiO2 spheres spray-coated surfaces showed better superhydrophobicity and superoleophobcity properties than the corresponding solid C@SiO2 coated surface. This study further demonstrated that superamphiphobicity depends on two critical factors, namely a cavity- and spot-rich hierarchical structure and the size and shape of overhangs. Moreover, the optimal conditions for the preparation of hollow SiO2 coated glass slide were identified after a systematic investigation of various concentrations of the carbon precursor and tetraethylorthosilicate. It was found that when 0.10 g carbon spheres prepared from 1.0 M carbon precursor were used as the template and 20 mg/mL tetraethylorthosilicate was used as silica precursor, the hollow SiO2 coated glass slide exhibited the best superamphiphobic performance, with the highest contact angles and lowest sliding angles for various liquids, such as water, olive oil, n-hexadecane and n-dodecane.

  10. Effects of plasmonic coupling and electrical current on persistent photoconductivity of single-layer graphene on pristine and silver-nanoparticle-coated SiO2/Si.

    PubMed

    Liu, Chih-Yi; Liang, Kengchih; Chang, Chun-Cheng; Tzeng, Yonhua

    2012-09-24

    Effects and mechanisms of conductivity variation of chemically vapor deposited single-layer graphene covering silver nanoparticles on SiO(2)/Si are reported based on blue-light (405 nm) induced plasmonic coupling and electrical current induced annealing and desorption of surface adsorbates. With 1V applied voltage, photoconductivity is positive except a brief negative period when the graphene is first illuminated by light. At 10 mV applied voltage, negative photoconductivity persists for hours. In comparison, negative photoconductivity of graphene on pristine SiO(2)/Si persists for tens of hours. When the applied voltage is increased to 1V, it takes tens of hours of light illumination to change to positive photoconductivity.

  11. Casimir frictional drag force between a SiO2 tip and a graphene-covered SiO2 substrate

    NASA Astrophysics Data System (ADS)

    Volokitin, A. I.

    2016-12-01

    The possibility of the mechanical detection of the Casimir friction using noncontact force microscope is discussed. On a SiO2 tip situated above a graphene-covered SiO2 substrate will act the frictional drag force mediated by a fluctuating electromagnetic field produced by a current in the graphene sheet. This friction force will produce the bending of the cantilever, which can be measured by state-of-art noncontact force microscope. Both the thermal and quantum contributions to the Casimir frictional drag force can be studied using this experimental setup. This result paves the way for the mechanical detection of the Casimir friction and for the application of the frictional drag effect in micro- and nanoelectromechanical devices (MEMS and NEMS).

  12. Preliminary results on the photo-transferred thermoluminescence from Ge-doped SiO2 optical fiber

    NASA Astrophysics Data System (ADS)

    Zulkepely, Nurul Najua; Amin, Yusoff Mohd; Md Nor, Roslan; Bradley, D. A.; Maah, Mohd Jamil; Mat Nawi, Siti Nurasiah; Wahib, Nur Fadira

    2015-12-01

    A study is made of photo-transferred thermoluminescence (PTTL), the TL being induced by transferring charge carriers from deeper to more superficial traps through energetic light exposure. Potential applications include dose reassessment in radiation dosimetry and also as a useful tool for dating. With incomplete emptying of deep traps following first readout, subsequent UV exposure is shown to lead to charge transfer to more shallow traps. Using Ge-doped SiO2 optical fibers exposed to 60Co gamma rays, the PTTL from the medium has been characterized in terms of the stimulation provided by exposure to a UV lamp and duration of exposure, maximum read-out temperature and pre-gamma irradiation dose. Ge-doped SiO2 optical fibers of flat cross-sectional shape have been used in this study. The efficiency of dose reassessment was compared to that of the highly popular phosphor-based TL detector TLD-100. Results show the maximum temperature of readout to have no measurable effect on the PTTL signal. For doses from 20 to 500 cGy, the method is shown to be effective using a UV lamp of wavelength 254 nm, also being indicative of potential application for doses on either side of the range currently investigated. A study was also made of the effect of UV exposure time on PTTL, seeking to determine the greatest accessible sensitivity and lowest measurable dose.

  13. A facile and cheap coating method to prepare SiO2/melamine-formaldehyde and SiO2/urea-formaldehyde composite microspheres

    NASA Astrophysics Data System (ADS)

    Mou, Shaoyan; Lu, Yao; Jiang, Yong

    2016-10-01

    A facile and cheap coating route has been explored to prepare SiO2/melamine formaldehyde hybrid particles. In this process, SiO2 microspheres act as seeds, and a polycondensation reaction occurs on the surface of melamine-formaldehyde pre-polymers. Formaldehyde is essential in this coating process because it acts as a novel and cheap surface modification agent instead of a traditional silane coupling agent. Ultrasonic method is used in the synthesis to avoid aggregation of nano- and micro-particles. Most of the traditional methods preparing composite microspheres were implemented under difficult conditions and at high costs. The improved coating method is much more able to provide a convenient path for researchers and engineers to more easily and economically perform experiments and engage in manufacturing. To verify this convenient method, SiO2/urea-formaldehyde composite microspheres were also prepared. SEM images show that the surfaces of all the products are smooth and well-shaped.

  14. Photocatalysis applications of some hybrid polymeric composites incorporating TiO2 nanoparticles and their combinations with SiO2/Fe2O3.

    PubMed

    Chibac, Andreea Laura; Buruiana, Tinca; Melinte, Violeta; Buruiana, Emil C

    2017-01-01

    Polymer nanocomposites containing titanium oxide nanoparticles (TiO2 NPs) combined with other inorganic components (Si-O-Si or/and γ-Fe2O3) were prepared by the dispersion of premade NPs (nanocrystalline TiO2, TiO2/SiO2, TiO2/Fe2O3, TiO2/SiO2/Fe2O3) within a photopolymerizable urethane dimethacrylate (polytetrahydrofuran-urethane dimethacrylate, PTHF-UDMA). The physicochemical characterization of nanoparticles and hybrid polymeric composites with 10 wt % NPs (S1-S4) was realized through XRD, TEM and FTIR analyses. The mean size (10-30 nm) and the crystallinity of the NPs varied as a function of the inorganic constituent. The catalytic activity of these hybrid films was tested for the photodegradation of phenol, hydroquinone and dopamine in aqueous solution under UV or visible-light irradiation. The best results were obtained for the films with TiO2/Fe2O3 or TiO2/SiO2/Fe2O3 NPs. The degradation of the mentioned model pollutants varied between 71% and 100% (after 250 min of irradiation) depending on the composition of the hybrid film tested and the light applied (UV-visible light). Also, it was established that such hybrid films can be reused at least for five cycles, without losing too much of the photocatalytic efficiency (ca. 7%). These findings could have implications in the development of new nanocatalysts.

  15. Photocatalysis applications of some hybrid polymeric composites incorporating TiO2 nanoparticles and their combinations with SiO2/Fe2O3

    PubMed Central

    Buruiana, Tinca; Melinte, Violeta; Buruiana, Emil C

    2017-01-01

    Polymer nanocomposites containing titanium oxide nanoparticles (TiO2 NPs) combined with other inorganic components (Si–O–Si or/and γ-Fe2O3) were prepared by the dispersion of premade NPs (nanocrystalline TiO2, TiO2/SiO2, TiO2/Fe2O3, TiO2/SiO2/Fe2O3) within a photopolymerizable urethane dimethacrylate (polytetrahydrofuran-urethane dimethacrylate, PTHF-UDMA). The physicochemical characterization of nanoparticles and hybrid polymeric composites with 10 wt % NPs (S1–S4) was realized through XRD, TEM and FTIR analyses. The mean size (10–30 nm) and the crystallinity of the NPs varied as a function of the inorganic constituent. The catalytic activity of these hybrid films was tested for the photodegradation of phenol, hydroquinone and dopamine in aqueous solution under UV or visible-light irradiation. The best results were obtained for the films with TiO2/Fe2O3 or TiO2/SiO2/Fe2O3 NPs. The degradation of the mentioned model pollutants varied between 71% and 100% (after 250 min of irradiation) depending on the composition of the hybrid film tested and the light applied (UV–visible light). Also, it was established that such hybrid films can be reused at least for five cycles, without losing too much of the photocatalytic efficiency (ca. 7%). These findings could have implications in the development of new nanocatalysts. PMID:28243566

  16. Double-faced γ-Fe2O3||SiO2 nanohybrids: flame synthesis, in situ selective modification and highly interfacial activity

    NASA Astrophysics Data System (ADS)

    Li, Yunfeng; Hu, Yanjie; Jiang, Hao; Li, Chunzhong

    2013-05-01

    Double-faced γ-Fe2O3||SiO2 nanohybrids (NHs) and their in situ selective modification on silica faces with the 3-methacryloxypropyltrimethoxysilane molecules have been successfully prepared by a simple, rapid and scalable flame aerosol route. The double-faced NHs perfectly integrate magnetic hematite hemispheres and non-magnetic silica parts into an almost intact nanoparticle as a result of phase segregation during the preparation process. The unique feature allows us to easily manipulate these particles into one-dimensional chain-like nanostructures. On the other hand, in situ selectively modified double-faced γ-Fe2O3||SiO2 NHs possess excellent interfacial activities, which can assemble into many interesting architectures, such as interfacial film, magnetic responsive capsules, novel magnetic liquid marbles and so forth. The modified NHs prefer to assemble at the interface of water-oil or oil-water systems. It is believed that the highly interfacial active NHs are not only beneficial for the development of interface reaction in a miniature reactor, but also very promising functional materials for other smart applications.Double-faced γ-Fe2O3||SiO2 nanohybrids (NHs) and their in situ selective modification on silica faces with the 3-methacryloxypropyltrimethoxysilane molecules have been successfully prepared by a simple, rapid and scalable flame aerosol route. The double-faced NHs perfectly integrate magnetic hematite hemispheres and non-magnetic silica parts into an almost intact nanoparticle as a result of phase segregation during the preparation process. The unique feature allows us to easily manipulate these particles into one-dimensional chain-like nanostructures. On the other hand, in situ selectively modified double-faced γ-Fe2O3||SiO2 NHs possess excellent interfacial activities, which can assemble into many interesting architectures, such as interfacial film, magnetic responsive capsules, novel magnetic liquid marbles and so forth. The modified NHs

  17. Enhanced adsorptive removal of toxic dyes using SiO2 nanofibers

    NASA Astrophysics Data System (ADS)

    Batool, S. S.; Imran, Z.; Hassan, Safia; Rasool, Kamran; Ahmad, Mushtaq; Rafiq, M. A.

    2016-05-01

    Electrospinning method was used to synthesize porous SiO2 nanofibers. The adsorption of Methyl Orange and Safranin O by porous SiO2 nanofibers was carried out by varying the parameters such as pH, contact time, adsorbent dose, dye concentration, and temperature. Equilibrium adsorption data followed Langmuir isotherms. Kinetic adsorption followed second-order rate kinetics model. The maximum adsorption capacity for Methyl Orange and Safranin O was found to be 730.9 mg/g and 960.4 mg/g, respectively. Acidic pH was favorable for the adsorption of Methyl Orange while basic pH was favorable for the adsorptions of Safranin O. Modeling study suggested the major mode of adsorption, while thermodynamic study showed the endothermic reactions. This effort has pronounced impact on environmental applications of SiO2 nanofibers as auspicious adsorbent nanofibers for organic material from aqueous solution.

  18. Effect of water layer at the SiO2/graphene interface on pentacene morphology.

    PubMed

    Chhikara, Manisha; Pavlica, Egon; Matković, Aleksandar; Gajić, Radoš; Bratina, Gvido

    2014-10-07

    Atomic force microscopy has been used to examine early stages of pentacene growth on exfoliated single-layer graphene transferred to SiO2 substrates. We have observed 2D growth with mean height of 1.5 ± 0.2 nm on as-transferred graphene. Three-dimensional islands of pentacene with an average height of 11 ± 2 nm were observed on graphene that was annealed at 350 °C prior to pentacene growth. Compellingly similar 3D morphology has been observed on graphene transferred onto SiO2 that was treated with hexamethyldisilazane prior to the transfer of graphene. On multilayer graphene we have observed 2D growth, regardless of the treatment of SiO2. We interpret this behavior of pentacene molecules in terms of the influence of the dipolar field that emerges from the water monolayer at the graphene/SiO2 interface on the surface energy of graphene.

  19. Dispersion effects in SiO2 polymorphs: An ab initio study

    NASA Astrophysics Data System (ADS)

    Hay, Henri; Ferlat, Guillaume; Casula, Michele; Seitsonen, Ari Paavo; Mauri, Francesco

    2015-10-01

    The effect of electronic dispersion over a wide variety of SiO2 polymorphs (faujasite, ferrierite, α -cristobalite, α -quartz, coesite, and stishovite) is investigated using state-of-the-art density functional theory. Different functionals and dispersion correction schemes are compared, ranging from the local density approximation to fully nonlocal exchange-correlation functionals. It is shown that both empirical dispersion corrections and fully nonlocal functionals improve the energetics and give correct volumetric data. However, the correct volume results come from error cancellation between an overestimation of the Si-O distance and an underestimation of the Si-O-Si angle. Quantum Monte Carlo is used to compute the quartz-cristobalite energy difference within an accuracy of 0.2 kCal/mol per SiO2 unit. This demonstrates the feasability of achieving subchemical accuracy on extended systems, and confirms the validity of the Slater-Jastrow ansatz for describing SiO2 polymorphs.

  20. Investigation on mechanical losses in TiO2/SiO2 dielectric coatings

    NASA Astrophysics Data System (ADS)

    Amico, P.; Bosi, L.; Cottone, F.; Dari, A.; Gammaitoni, L.; Marchesoni, F.; Punturo, M.; Travasso, F.; Vocca, H.

    2006-03-01

    Interferometric gravitational wave detectors use test masses made by large mirrors whose coating is usually made by multiple layers of dielectric materials, most commonly alternating layers of SiO2 (silica) and Ta2O5 (tantala). It is foreseeable that in future interferometric gravitational wave detector projects (LCGT, EGO, VIRGO,), the mirrors will be cooled down to cryogenic temperature in order to reduce the noise generated by the thermally activated motion of the masses. However, low temperature mechanical losses in the Ta2O5/SiO2 coatings might limit the design sensitivity for such cryogenic detectors by setting a lower limit for the expected thermal noise. Here we present some measurements of mechanical losses in the TiO2/SiO2 coatings at room and low temperature (80K-300K).

  1. Preparations and properties of a tunable void with shell thickness SiO2@SiO2 core-shell structures via activators generated by electron transfer for atom transfer radical polymerization

    NASA Astrophysics Data System (ADS)

    Ren, Yi-xian; Zhou, Guo-wei; Cao, Pei

    2016-02-01

    Core-shell structure nanoparticles are attracting considerable attention because of their applications in drug delivery, catalysis carrier, and nanomedicine. In this study, SiO2@SiO2 core-shell structure with tunable void and shell thickness was successfully prepared for the first time using SiO2-poly(buty acrylate) (PBA)-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) (SiO2-PBA-b-PDMAEMA) as the template and tetraethoxysilane (TEOS) as the silica source. An amphiphilic copolymer PBA-b-PDMAEMA was first grafted onto the SiO2 nanosphere surface through activators regenerated by electron transfer for atom transfer radical polymerization. TEOS was hydrolyzed along with the PDMAEMA chain through hydrogen bonding, and the core-shell structure of SiO2@SiO2 was obtained through calcination to remove the copolymer. The gradient hydrophilicity of the PBA-b-PDMAEMA copolymer template facilitated the hydrolysis of TEOS molecules along the PDMAEMA to PBA segments, thereby tuning the voids between the SiO2 core and SiO2 shell, as well as the SiO2 shell thickness. The voids were about 10-15 nm and the shell thicknesses were about 4-11 nm when adding different amounts of DMAEMA monomer. SiO2@SiO2 core-shell structures with tunable void and shell thickness were employed as supports for the loading and release of doxorubicin hydrochloride (DOX) in PBS (pH 4.0). The samples demonstrated good loading capacity and controlled release rate of DOX.

  2. Electric-Field-Induced Amplitude Tuning of Ferromagnetic Resonance Peak in Nano-granular Film FeCoB-SiO2/PMN-PT Composites

    NASA Astrophysics Data System (ADS)

    Luo, Mei; Zhou, Peiheng; Liu, Yunfeng; Wang, Xin; Xie, Jianliang

    2016-11-01

    One of the challenges in the design of microwave absorbers lies in tunable amplitude of dynamic permeability. In this work, we demonstrate that electric-field-induced magnetoelastic anisotropy in nano-granular film FeCoB-SiO2/PMN-PT (011) composites can be used to tune the amplitude of ferromagnetic resonance peak at room temperature. The FeCoB magnetic particles are separated from each other by SiO2 insulating matrix and present slightly different in-plane anisotropy fields. As a result, multi-resonances appear in the imaginary permeability ( μ″) curve and mixed together to form a broadband absorption peak. The amplitude of the resonance peak could be modulated by external electric field from 118 to 266.

  3. Electric-Field-Induced Amplitude Tuning of Ferromagnetic Resonance Peak in Nano-granular Film FeCoB-SiO2/PMN-PT Composites.

    PubMed

    Luo, Mei; Zhou, Peiheng; Liu, Yunfeng; Wang, Xin; Xie, Jianliang

    2016-12-01

    One of the challenges in the design of microwave absorbers lies in tunable amplitude of dynamic permeability. In this work, we demonstrate that electric-field-induced magnetoelastic anisotropy in nano-granular film FeCoB-SiO2/PMN-PT (011) composites can be used to tune the amplitude of ferromagnetic resonance peak at room temperature. The FeCoB magnetic particles are separated from each other by SiO2 insulating matrix and present slightly different in-plane anisotropy fields. As a result, multi-resonances appear in the imaginary permeability (μ″) curve and mixed together to form a broadband absorption peak. The amplitude of the resonance peak could be modulated by external electric field from 118 to 266.

  4. Role of SiO2 coating in multiferroic CoCr2O4 nanoparticles

    NASA Astrophysics Data System (ADS)

    Kamran, M.; Ullah, Asmat; Mehmood, Y.; Nadeem, K.; Krenn, H.

    2017-02-01

    Effect of silica (SiO2) coating concentration on structural and magnetic properties of multiferroic cobalt chromite (CoCr2O4) nanoparticles have been studied. The nanoparticles with average crystallite size in the range 19 to 28 nm were synthesised by sol-gel method. X-ray diffraction (XRD) analysis has verified the composition of single-phase cubic normal spinel structure of CoCr2O4 nanoparticles. The average crystallite size and cell parameter decreased with increasing SiO2 concentration. TEM image revealed that the shape of nanoparticles was non-spherical. Zero field cooled/field cooled (ZFC/FC) curves revealed that nanoparticles underwent a transition from paramagnetic (PM) state to collinear short-range ferrimagnetic (FiM) state, and this PM-FiM transition temperature decreased from 101 to 95 K with increasing SiO2 concentration or decreasing crystallite size. A conical spin state at Ts = 27 K was also observed for all the samples which decreased with decreasing average crystallite size. Low temperature lock-in transition was also observed in these nanoparticles at 12 K for uncoated nanoparticles which slightly shifted towards low temperature with decreasing average crystallite size. Saturation magnetization (Ms) showed decreasing trend with increasing SiO2 concentration, which was due to decrease in average crystallite size of nanoparticles and enhanced surface disorder in smaller nanoparticles. The temperature dependent AC-susceptibility also showed the decrease in the transition temperature (Tc), broadening of the Tc peak and decrease in magnetization with increasing SiO2 concentration or decreasing average crystallite size. In summary, the concentration of SiO2 has significantly affected the structural and magnetic properties of CoCr2O4 nanoparticles.

  5. Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films

    SciTech Connect

    Hellman, Frances

    1998-10-03

    OAK B204 Growth Induced Magnetic Anisotropy in Crystalline and Amorphous Thin Films. The work in the past 6 months has involved three areas of magnetic thin films: (1) amorphous rare earth-transition metal alloys, (2) epitaxial Co-Pt and hTi-Pt alloy thin films, and (3) collaborative work on heat capacity measurements of magnetic thin films, including nanoparticles and CMR materials.

  6. Who's on first? Tracking in real time the growth of multiple crystalline phases of an organic semiconductor: Tetracene on SiO2

    NASA Astrophysics Data System (ADS)

    Nahm, R. K.; Engstrom, J. R.

    2017-02-01

    We have examined the effect of growth rate on the evolution of two polymorphs of thin films of tetracene on SiO2 using synchrotron X-ray radiation and molecular beam techniques. Ex situ X-ray reflectivity shows that tetracene forms two phases on SiO2: a thin-film phase and a bulk phase. We have used in situ, real-time grazing incidence diffraction during growth to reveal the nature of growth concerning these two phases. We observe that there is initially growth of only the thin-film phase, up to a thickness of several monolayers. This is followed by the nucleation of the bulk phase, growth of both phases, and finally growth of only the bulk phase. We find that the deposited thickness when the bulk phase nucleates increases with increasing growth rate. Similarly, we find that the deposited thickness at which the thin-film phase saturates also increases with increasing growth rate. These apparent dependencies on growth rate are actually a consequence of the local coverage, which depends on growth rate, particularly for the former effect. At low growth rates, there is 3D growth resulting from the upward transport of tetracene at island edges, resulting in tall features where molecules escape the influence of the substrate and form into the bulk phase. Increasing the growth rate leads to growth that is more 2D and uniform in coverage, delaying the formation of the bulk phase.

  7. Interfacial charge trapping in extrinsic Y2O3/SiO2 bilayer gate dielectric based MIS devices on Si(100)

    NASA Astrophysics Data System (ADS)

    Rastogi, A. C.; Sharma, R. N.

    2001-08-01

    Metal-insulator-semiconductor (MIS) structures based on an extrinsic Y2O3 dielectric film on Si show high leakage currents due to roughness-related highly localized fields. Oxygen annealing increases the dielectric constant and strength and reduces leakage currents by transforming Y2O3 (film)/Si(100) into a bilayer Y2O3 (film)/SiO2/Si(100) dielectric structure. Evolution of interfacial SiO2 causes generation of mid-gap interface states at Ev + 0.23 eV and Ev + 0.43 eV, which act as electron traps and are responsible for hysteresis effects in capacitance-voltage (C-V) and current-voltage (I-V) behaviour in the accumulation-inversion modes. The electron trapping reduces the cathodic field and causes lowering of the current and the shift in current to higher fields after successive ramps. The charge trapping effects cause varied and unstable C-V and I-V behaviour of MIS structures based on a Y2O3/SiO2 bilayer gate dielectric. Its origin has been attributed to microstructure and defect state modification at the Y2O3 film-Si interface. This limits its application in high-density dynamic random access memory and ultra-large-scale integration devices.

  8. Who's on first? Tracking in real time the growth of multiple crystalline phases of an organic semiconductor: Tetracene on SiO2.

    PubMed

    Nahm, R K; Engstrom, J R

    2017-02-07

    We have examined the effect of growth rate on the evolution of two polymorphs of thin films of tetracene on SiO2 using synchrotron X-ray radiation and molecular beam techniques. Ex situ X-ray reflectivity shows that tetracene forms two phases on SiO2: a thin-film phase and a bulk phase. We have used in situ, real-time grazing incidence diffraction during growth to reveal the nature of growth concerning these two phases. We observe that there is initially growth of only the thin-film phase, up to a thickness of several monolayers. This is followed by the nucleation of the bulk phase, growth of both phases, and finally growth of only the bulk phase. We find that the deposited thickness when the bulk phase nucleates increases with increasing growth rate. Similarly, we find that the deposited thickness at which the thin-film phase saturates also increases with increasing growth rate. These apparent dependencies on growth rate are actually a consequence of the local coverage, which depends on growth rate, particularly for the former effect. At low growth rates, there is 3D growth resulting from the upward transport of tetracene at island edges, resulting in tall features where molecules escape the influence of the substrate and form into the bulk phase. Increasing the growth rate leads to growth that is more 2D and uniform in coverage, delaying the formation of the bulk phase.

  9. Optimizing conditions of preparation of thermoresponsive SiO2-POEGMA particles via AGET-ATRP

    NASA Astrophysics Data System (ADS)

    Du, Zhiping; Sun, Xiaofeng; Tai, Xiumei; Wang, Guoyong; Liu, Xiaoying

    2015-02-01

    Thermosensitive poly(ethylene glycol) methyl ether methacrylate (POEGMA) was grafted on SiO2 nanoparticles using activators generated by electron transfer atom transfer radical polymerization (AGET-ATRP) technique. The effects of the amount of ligand, catalyst, ascorbic acid and monomer, as well as the reaction temperature and time were systematically investigated and optimized to get a high grafting density. The structure of the hybrid materials was characterized by Fourier transform infrared (FTIR) spectroscopy, and the morphology was characterized by transmission electron microscopy (TEM) observations. Thermosensitive properties of SiO2-POEGMA particles were investigated at different grafting densities by turbidity measurements.

  10. Preparation of SiO2 nanowires from rice husks by hydrothermal method and the RNA purification performance

    NASA Astrophysics Data System (ADS)

    Huang, Meiyan; Cao, Jianping; Meng, Xing; Liu, Yangsi; Ke, Wei; Wang, Jialiang; Sun, Ling

    2016-10-01

    In this study, SiO2 nanowires were prepared by using rice husks as silicon source via a hydrothermal method. The microstructure, thermal stability and morphology of SiO2 nanowires were characterized by X-ray diffraction, infrared spectroscopy, thermal gravimetric analysis and scanning electron microscope. SiO2 nanowires with a diameter of 30-100 nm were obtained and the formation mechanism of SiO2 nanowires during the hydrothermal reaction was proposed. The SiO2 nanowires were introduced into membrane spin columns to isolate RNA and the values of A260/280 and A260/230 were 2.0-2.1 and 1.8-2.0, respectively, which shows the SiO2 nanowires were effective for RNA purification.

  11. Effect of SiO2-acryl nanohybrid coating layers on transparent conducting oxide-poly(ethylene terephthalate) superstrate.

    PubMed

    Kang, Y T; Kang, D P; Kang, D J; Chung, I D

    2013-05-01

    SiO2-acryl nanohybrid coating layers were produced by hybridizing acrylic resin and surface-modified colloidal silica (CS) nanoparticles. First, CS nanoparticles were modified with methyltrimethoxysilane (MTMS) and vinyltrimethoxysilane (VTMS) by a sol-gel process. The surface-modified CS nanoparticles were then solvent-exchanged to be homogeneous in acrylic resin. The Hybrid materials were mixed in variation with the amount of surface-modified CS nanoparticles, coated with poly(ethylene terephthalate) (PET), then finally cured by UV light to obtain a hybrid coating layer. Field emission scanning electron microscopy (FE-SEM), particle size analysis (using a Zetasizer), and atomic force microscopy (AFM) were performed to determine the morphology of the hybrid thin-films. Thermogravimetric analysis (TGA) was used to investigate the thermal properties. Fourier-transform infrared (FTIR), ultraviolet-visible (UVNis) spectroscopies, and pencil hardness were used to obtain the details of chemical structures, optical properties, and hardness, respectively. The hybrid thin films had shown to be enhanced properties compared to their urethane acrylate prepolymer (UAP) coating film.

  12. Preparation and morphological and optical characterization of azo-polymer-based SiO2 sonogel hybrid composites

    NASA Astrophysics Data System (ADS)

    Morales-Saavedra, Omar G.; Ontiveros-Barrera, Fernando G.; Torres-Zúñiga, Vicente; Guadalupe-Bañuelos, José; Ortega-Martínez, Roberto; Rivera, Ernesto; García, Tonatiuh

    2009-08-01

    The well-established catalyst-free sonogel route was successfully implemented to fabricate highly pure, optically active, solid state polymeric azo- dye/SiO2-based hybrid composites. Bulk samples exhibit controllable geometrical shapes and monolithic structure with variable dopant concentrations. Since the implemented azo-dye chromophores exhibit a push-pull structure, hybrid film samples were spin-coated on ITO-covered glass substrates; molecular alignment was then performed via electrical poling in order to explore the quadratic nonlinear optical performance of this kind of composite. Comprehensive morphological, spectroscopic and optical characterization of the samples were performed with several experimental techniques: atomic force microscopy, x-ray diffraction and infrared, Raman, photoluminescent and ultraviolet-visible spectroscopies. The linear refractive indices of both bulk and thin film samples were measured according to the Brewster angle technique and a numerical analysis of the transmission spectral data, respectively. Regardless of the low glass transition temperatures of the studied polymers, some hybrid film samples were able to display stable nonlinear optical activity such as second harmonic generation. Results show that the chromophores were satisfactorily embedded into the highly pure SiO2 sonogel network without significant guest-host molecular interactions, thus preserving their optical properties and producing sol-gel hybrid glasses suitable for optical applications.

  13. Toward intrinsic graphene surfaces: a systematic study on thermal annealing and wet-chemical treatment of SiO2-supported graphene devices.

    PubMed

    Cheng, Zengguang; Zhou, Qiaoyu; Wang, Chenxuan; Li, Qiang; Wang, Chen; Fang, Ying

    2011-02-09

    By combining atomic force microscopy and trans-port measurements, we systematically investigated effects of thermal annealing on surface morphologies and electrical properties of single-layer graphene devices fabricated by electron beam lithography on silicon oxide (SiO(2)) substrates. Thermal treatment above 300 °C in vacuum was required to effectively remove resist residues on graphene surfaces. However, annealing at high temperature was found to concomitantly bring graphene in close contact with SiO(2) substrates and induce increased coupling between them, which leads to heavy hole doping and severe degradation of mobilities in graphene devices. To address this problem, a wet-chemical approach employing chloroform was developed in our study, which was shown to enable both intrinsic surfaces and enhanced electrical properties of graphene devices. Upon the recovery of intrinsic surfaces of graphene, the adsorption and assisted fibrillation of amyloid β-peptide (Aβ1-42) on graphene were electrically measured in real time.

  14. Synthesis of carbon encapsulated SiO2 nanoparticles from rice husk and its application in solar to steam conversion

    NASA Astrophysics Data System (ADS)

    Mufti, Nandang; Lestari, Nurhayati A.; Suciani, Erlin; Fuad, Abdulloh; Diantoro, Markus

    2016-03-01

    Steam is important in many technological applications including sterilization of medical devices, cleaning, and power generating. In general, steam can be produced by boiling water at high temperature. In new technology, solar can convert water directly into steam even at low temperature by using nanoparticles. In this research we study solar to steam conversion of carbon encapsulated SiO2 nanoparticles (SiO2@C) synthesized from rice husk. SiO2 nanoparticles were synthesized using alkali extraction and sol-gel methods. While synthesis of carbon encapsulated SiO2 nanoparticles was done by sonochemical method with glucose as source of carbon. The samples have been characterized by XRF, SEM-EDX, and XRD. The effectivity of solar steam conversion performed by measuring time dependent of temperature and pressure. XRF and XRD results shown that SiO2 nanoparticles have purity of 97.2% inn amorphous phase. Carbon encapsulated SiO2 nanoparticles (SiO2@C) have successfully synthesized indicating by NaOH base test. The morphology of SiO2@C is agglomerated with average particle size around 20 nm. The measurement of solar to steam conversion showed that increasing carbon concentration of SiO2@C rises steam production with indicated by increasing temperature and pressure of steam.

  15. Angular dependence of SiO2 etch rate at various bias voltages in a high density CHF3 plasma

    NASA Astrophysics Data System (ADS)

    Lee, Gyeo-Re; Hwang, Sung-Wook; Min, Jae-Ho; Moon, Sang Heup

    2002-09-01

    The dependence of the SiO2 etch rate on the angle of ions incident on the substrate surface was studied over a bias voltage range from -20 to -600 V in a high-density CHF3 plasma using a Faraday cage to control the ion incident angle. The effect of the bottom plane on the sidewall etching was also examined. Differences in the characteristics of the etch rate as a function of the ion angle were observed for different bias voltage regions. When the absolute value of the bias voltage was smaller than 200 V, the normalized etch rate (NER) defined as the etch rate normalized by the rate on the horizontal surface, changed following a cosine curve with respect to the ion incident angle, defined as the angle between the ion direction and the normal of the substrate surface. When the magnitude of the bias voltage was larger than 200 V, the NER was deviated to higher values from those given by a cosine curve at ion angles between 30deg and 70deg, and then drastically decreased at angles higher than 70deg until a net deposition was observed at angles near 90deg. The characteristic etch-rate patterns at ion angles below 70deg were determined by the ion energy transferred to the surface, which affected the SiO2 etch rate and, simultaneously, the rate of removal of a fluorocarbon polymer film formed on the substrate surface. At high ion angles, particles emitted from the bottom plane contributed to polymer formation on and affected the etching characteristics of the substrate. copyright 2002 American Vacuum Society.

  16. Crystallization kinetics of BaO-Al2O3-SiO2 glasses

    NASA Technical Reports Server (NTRS)

    Bansal, Narottam P.; Hyatt, Mark J.

    1988-01-01

    Barium aluminosilicate glasses are being investigated as matrix materials in high-temperature ceramic composites for structural applications. Kinetics of crystallization of two refractory glass compositions in the barium aluminosilicate system were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). From variable heating rate DTA, the crystallization activation energies for glass compositions (wt percent) 10BaO-38Al2O3-51SiO2-1MoO3 (glass A) and 39BaO-25Al2O3-35SiO2-1MoO3 (glass B) were determined to be 553 and 558 kJ/mol, respectively. On thermal treatment, the crystalline phases in glasses A and B were identified as mullite (3Al2O3-2SiO2) and hexacelsian (BaO-Al2O3-2SiO2), respectively. Hexacelsian is a high-temperature polymorph which is metastable below 1590 C. It undergoes structural transformation into the orthorhombic form at approximately 300 C accompanied by a large volume change which is undesirable for structural applications. A process needs to be developed where stable monoclinic celsian, rather than hexacelsian, precipitates out as the crystal phase in glass B.

  17. Redox behavior of a ferrocene monolayer on SiO2 obtained after click-coupling

    NASA Astrophysics Data System (ADS)

    Aiello, V.; Joo, N.; Buckley, J.; Nonglaton, G.; Duclairoir, F.; Dubois, L.; Marchon, J. C.; Gély, M.; Chevalier, N.; De Salvo, B.

    2013-06-01

    Redox active ferrocene derivatives were grafted upon SiO2 surface via a carbon-based linker. The indirect grafting procedure consisted in a silanization followed by a click-chemistry reaction. This immobilization method of ethynyl-ferrocene yields a mixed organic/inorganic charge transfer modulation medium made of a C3 linker ended by a 1,2,3-triazole, bound to a thin SiO2 layer. Such a linker has never been tested before. Its use combines the advantages of a thin dielectric layer (SiO2+ > C3 linker) to the versatility of a two-step process that could easily be transferred to other sensitive or hard to synthesize compounds. Such organic/inorganic linker has been tested to tune the redox properties and charge transfer kinetics of the overall hybrid system and the results could be of importance for hybrid memory devices applications. Cyclic voltammetry studies conducted on this hybrid system were indeed used to confirm ferrocene immobilization, determine the molecular surface coverage and study the redox charge/discharge kinetics. The obtained results show the good surface coverage and charge retention properties, achieved by grafting upon SiO2 via a > C3 linker. For comparison, the ferrocene compound was also immobilized on Si (C2 linker).

  18. Microscopical and mechanical evaluation of the durability of SiO2 aggregates

    NASA Astrophysics Data System (ADS)

    El Bahraoui, Hassan; Khouchaf, Lahcen; Ben Fraj, Amor

    2016-05-01

    The durability of SiO2 compounds is closely related to its structural properties. In this work three natural siliceous aggregates (called G1, G2 and G3) are studied. Improvement of the durability of the starting material leads to a significant energy savings by extending the lifetime of structures. The chemical composition of the three natural aggregates shows that G1 and G2 have almost the same chemical composition (SiO2) and G3 is different and contains SiO2 quartz type and calcite as major components (SiO2, calcite and dolomite). X-ray diffraction (XRD) shows that natural aggregates G1 is more crystallized than G2 and G3. After alkali silica reaction (ASR) process, the reactivity of G3 aggregate seems to be higher than the G1 and G2 aggregates. The mechanical results show the slight difference between mortar containing G1 (M_G1) and that containing G2 (M_G2). Their compressive strength is 10% less than that of reference (M_SS). As it is more reactive, G3 seems improving the compressive strength of M_G3, compared to M_G1 and M_G2. Contribution to the topical issue "Materials for Energy Harvesting, Conversion and Storage (ICOME 2015) - Elected submissions", edited by Jean-Michel Nunzi, Rachid Bennacer and Mohammed El Ganaoui

  19. Location and Electronic Nature of Phosphorus in the Si Nanocrystal − SiO2 System

    PubMed Central

    König, Dirk; Gutsch, Sebastian; Gnaser, Hubert; Wahl, Michael; Kopnarski, Michael; Göttlicher, Jörg; Steininger, Ralph; Zacharias, Margit; Hiller, Daniel

    2015-01-01

    Up to now, no consensus exists about the electronic nature of phosphorus (P) as donor for SiO2-embedded silicon nanocrystals (SiNCs). Here, we report on hybrid density functional theory (h-DFT) calculations of P in the SiNC/SiO2 system matching our experimental findings. Relevant P configurations within SiNCs, at SiNC surfaces, within the sub-oxide interface shell and in the SiO2 matrix were evaluated. Atom probe tomography (APT) and its statistical evaluation provide detailed spatial P distributions. For the first time, we obtain ionisation states of P atoms in the SiNC/SiO2 system at room temperature using X-ray absorption near edge structure (XANES) spectroscopy, eliminating structural artefacts due to sputtering as occurring in XPS. K energies of P in SiO2 and SiNC/SiO2 superlattices (SLs) were calibrated with non-degenerate P-doped Si wafers. results confirm measured core level energies, connecting and explaining XANES spectra with h-DFT electronic structures. While P can diffuse into SiNCs and predominantly resides on interstitial sites, its ionization probability is extremely low, rendering P unsuitable for introducing electrons into SiNCs embedded in SiO2. Increased sample conductivity and photoluminescence (PL) quenching previously assigned to ionized P donors originate from deep defect levels due to P. PMID:25997696

  20. Exotic SiO2H2 Isomers: Theory and Experiment Working in Harmony.

    PubMed

    McCarthy, Michael C; Gauss, Jürgen

    2016-05-19

    Replacing carbon with silicon can result in dramatic and unanticipated changes in isomeric stability, as the well-studied CO2H2 and the essentially unknown SiO2H2 systems illustrate. Guided by coupled-cluster calculations, three SiO2H2 isomers have been detected and spectroscopically characterized in a molecular beam discharge source using rotational spectroscopy. The cis,trans conformer of dihydroxysilylene HOSiOH, the ground-state isomer, and the high-energy, metastable dioxasilirane c-H2SiO2 are abundantly produced in a dilute SiH4/O2 electrical discharge, enabling precise structural determinations of both by a combination of isotopic measurements and calculated vibrational corrections. The isotopic studies also provide insight into their formation route, suggesting that c-H2SiO2 is formed promptly in the expansion but that cis,trans-HOSiOH is likely formed by secondary reactions following formation of the most stable dissociation pair, SiO + H2O. Although less abundant, the rotational spectrum of trans-silanoic acid, the silicon analogue of formic acid, HSi(O)OH, has also been observed.

  1. Nanoimprint lithography using TiO2-SiO2 ultraviolet curable materials

    NASA Astrophysics Data System (ADS)

    Takei, Satoshi

    2015-05-01

    Ultraviolet nanoimprint lithography has great potential for commercial device applications that are closest to production such as optical gratings, planar waveguides, photonic crystals, semiconductor, displays, solar cell panel, sensors, highbrightness LEDs, OLEDs, and optical data storage. I report and demonstrate the newly TiO2-SiO2 ultraviolet curable materials with 20-25 wt% ratio of high titanium for CF4/O2 etch selectivity using nanoimprint lithography process. The multiple structured three-dimensional micro- and nanolines patterns were observed to be successfully patterned over the large areas. The effect of titanium concentration on CF4/O2 etch selectivity with pattern transferring carbon layer imprinting time was investigated. CF4/O2 etching rate of the TiO2-SiO2 ultraviolet curable material was approximately 3.8 times lower than that of the referenced SiO2 sol-gel ultraviolet curable material. The TiO2-SiO2 ultraviolet curable material with high titanium concentration has been proved to be versatile in advanced nanofabrication.

  2. Enhanced photovoltaic performance of perovskite solar cells with mesoporous SiO2 scaffolds

    NASA Astrophysics Data System (ADS)

    Yu, Xiao; Chen, Si; Yan, Kai; Cai, Xin; Hu, Hsienwei; Peng, Ming; Chen, Buxin; Dong, Bin; Gao, Xue; Zou, Dechun

    2016-09-01

    We applied SiO2 nanoparticles as an alternative to mesoporous TiO2 or Al2O3 scaffolds and achieved power conversion efficiency (PCE) of up to 16.2%. Careful characterization of the effects of different scaffolds on device performance reveals that SiO2-based perovskite solar cells show much higher PCE due to the higher Voc and fill factor (FF), and the hysteresis for SiO2-based perovskite solar cell is less severe than for Al2O3-based perovskite solar cell. Time-correlated-single-photoncounting (TCSPC) luminescence decay and external quantum efficiency (EQE) tests provide further insights into the charge transfer behavior and light-harvesting characteristics of the proposed devices. Potential mechanisms of the observed phenomena are also suggested. Taken together, our results demonstrate that SiO2 nanoparticles may potentially replace mesoporous TiO2 or Al2O3 scaffolds in perovskite solar cells to achieve remarkably high PCE.

  3. Evaluation of physicochemical properties of SiO2-coated stainless steel after sterilization.

    PubMed

    Walke, Witold; Paszenda, Zbigniew; Pustelny, Tadeusz; Opilski, Zbigniew; Drewniak, Sabina; Kościelniak-Ziemniak, Magdalena; Basiaga, Marcin

    2016-06-01

    The study of most of the literature devoted to the use of coronary stents indicates that their efficiency is determined by the physicochemical properties of the implant surface. Therefore, the authors of this study suggested conditions for the formation of SiO2 layers obtained with the use of sol-gel methodology showing physicochemical properties adequate to the specific conditions of the cardio-vascular system. Previous experience of authors helped them much to optimize the coating of 316LVM steel surface with SiO2. The values of parameters that determine the usefulness of the coating in medical applications have been determined. In order to identify the phenomena taking place at the boundary of phases and to evaluate the usefulness of the proposed surface modification, taking into consideration the medical sterilization (steam or ethylene oxide (EO)), the potentiodynamic, impedance, adhesion, surface morphology and biological assessment characterizations were performed. Regardless of the usage of the sterilizing agent (steam, EO) the study showed the reduction of critical force causing layer's delamination. The research results of corrosion resistance study also confirmed a slight decrease of SiO2 barrier properties of the samples after sterilization in contact with the artificial plasma. SiO2 layers after the sterilization process did not show significant features of cytotoxicity and had no negative influence on blood cell counts, which confirmed the results of quantitative and qualitative studies.

  4. SiO2 nanofluid planar jet impingement cooling on a convex heated plate

    NASA Astrophysics Data System (ADS)

    Asghari Lafmajani, Neda; Ebrahimi Bidhendi, Mahsa; Ashjaee, Mehdi

    2016-12-01

    The main objective of this paper is to investigate the heat transfer coefficient of a planar jet of SiO2 nanofluid that impinges vertically on the middle of a convex heated plate for cooling purposes. The planar jet issues from a rectangular slot nozzle. The convex aluminum plate has a thickness, width and length of 0.2, 40 and 130 mm, respectively, and is bent with a radius of 200 mm. A constant heat-flux condition is employed. 7 nm SiO2 particles are added to water to prepare the nanofluid with 0.1, 1 and 2 % (ml SiO2/ml H2O) concentrations. The tests are also performed at different Reynolds numbers from 1803 to 2782. Results indicate that adding the SiO2 nanoparticles can effectively increase both local and average heat transfer coefficients up to 39.37 and 32.78 %, respectively. These positive effects often are more pronounced with increasing Reynolds numbers. This enhancement increases with ascending the concentration of nanofluid, especially from 0.1 to 1 %.

  5. The formation of diffraction gratings by the deposition of SiO2 colloidal microspheres

    NASA Astrophysics Data System (ADS)

    Ashurov, M. S.; Kazakova, T. A.; Stepanov, A. L.; Klimonsky, S. O.

    2016-12-01

    A simple way of fabrication of diffraction gratings with the help of deposition of SiO2 colloidal particles on vertical glass substrate has been proposed. The method is based on an intermittent, "stick-slip" motion of the suspension meniscus during liquid evaporation. The deposition was carried out at different temperatures (from 27 to 50 °C). Ethanol-based suspensions with a SiO2 concentration in the range of 0.2-0.83 g/L, both narrow-dispersed with SiO2 particle diameter of about 200-300 nm and polydisperse, were used. As a result, the structures consisting of parallel ridges of deposited SiO2 microspheres repeating with a period of 140-200 μm and empty gaps between them have been prepared. The diffraction gratings formation is possible only at temperatures higher than the critical value of about 30 °C, and their period enhances with the temperature increase. The real diffraction patterns of light have been obtained for such structures for the first time. Further modification of prepared structures with the purpose of their strengthening has been realized with the help of high-dose Ag+ implantation (4 × 1016 ions/cm2, ion energy of 30 keV) followed by sonication.

  6. Preparation of magnetic Fe3O4@SiO2 nanoparticles for immobilization of lipase.

    PubMed

    Liu, Wei; Zhou, Fang; Zhang, Xiao-Yun; Li, Yue; Wang, Xiang-Yu; Xu, Xi-Ming; Zhang, Ye-Wang

    2014-04-01

    Magnetic Fe3O4 nanoparticles were prepared with coprecipitatation method and covered with SiO2 to form the core-shell Fe3O4@SiO2 nanoparticles. Then the nanoparticles were modified with glutaradehyde for functionalization of the surface to aldehyde groups. The transmission electron microscopy confirmed the core-shell structure and revealed that the size of the nanoparticles was around 10 nm. It was observed that the lipase was immobilized on the nanoparticles successfully from the Fourier transform infrared spectra. The immobilized lipase on Fe3O4@SiO2 nanoparticles was characterized and compared to free enzyme. There are no significant differences observed in the optimal pH, temperature and Km before and after immobilization. However, the immobilized lipase displayed higher relative activity in the range of pH from 7.0 to 9.5. Compare with the free enzyme, the immobilized one showed higher thermal stability at temperature range from 30 to 70 degrees C, especially at high temperature. The relative activity of immobilized enzyme was 5.8 fold of the free lipase at 70 degrees C after 10 h incubation. Thus, the prepared lipase was proved to have the advantages like higher relative activity, better stability, broader pH range and easy to recovery. These results suggest that immobilization of lipase on Fe3O4@SiO2 nanoparticles has the potential industrial applications.

  7. Experimental Investigation of Thermal Performance of Miniature Heat Pipe Using SiO2-Water Nanofluids.

    PubMed

    Niu, Yan-Fang; Zhao, Wei-Lin; Gong, Yu-Ying

    2015-04-01

    The four miniature heat pipes filled with DI water and SiO2-water nanofluids containing different volume concentrations (0.2%, 0.6% and 1.0%) are experimentally measured on the condition of air and water cooling. The wall temperature and the thermal resistance are investigated for three inclination angles. At the same of inlet heat water temperature in the heat system, it is observed that the total wall temperatures on the evaporator section are almost retaining constant by air cooling and the wall temperatures at the front end of the evaporator section are slightly reduced by water cooling. However, the wall temperatures at the condenser section using SiO2-water nanofluids are all higher than that for DI water on the two cooling conditions. As compared with the heat pipe using DI water, the decreasing of the thermal resistance in heat pipe using nanofluids is about 43.10%-74.46% by air cooling and 51.43%-72.22% by water cooling. These indicate that the utilization of SiO2-water nanofluids as working fluids enhances the performance of the miniature heat pipe. When the four miniature heat pipes are cut to examine at the end of the experiment, a thin coating on the surface of the screen mesh of the heat pipe using SiO2-water nanofluids is found. This may be one reason for reinforcing the heat transfer performance of the miniature heat pipe.

  8. Characterization of ion-assisted induced absorption in A-Si thin-films used for multivariate optical computing

    NASA Astrophysics Data System (ADS)

    Nayak, Aditya B.; Price, James M.; Dai, Bin; Perkins, David; Chen, Ding Ding; Jones, Christopher M.

    2015-06-01

    Multivariate optical computing (MOC), an optical sensing technique for analog calculation, allows direct and robust measurement of chemical and physical properties of complex fluid samples in high-pressure/high-temperature (HP/HT) downhole environments. The core of this MOC technology is the integrated computational element (ICE), an optical element with a wavelength-dependent transmission spectrum designed to allow the detector to respond sensitively and specifically to the analytes of interest. A key differentiator of this technology is it uses all of the information present in the broadband optical spectrum to determine the proportion of the analyte present in a complex fluid mixture. The detection methodology is photometric in nature; therefore, this technology does not require a spectrometer to measure and record a spectrum or a computer to perform calculations on the recorded optical spectrum. The integrated computational element is a thin-film optical element with a specific optical response function designed for each analyte. The optical response function is achieved by fabricating alternating layers of high-index (a-Si) and low-index (SiO2) thin films onto a transparent substrate (BK7 glass) using traditional thin-film manufacturing processes (e.g., ion-assisted e-beam vacuum deposition). A proprietary software and process are used to control the thickness and material properties, including the optical constants of the materials during deposition to achieve the desired optical response function. The ion-assisted deposition is useful for controlling the densification of the film, stoichiometry, and material optical constants as well as to achieve high deposition growth rates and moisture-stable films. However, the ion-source can induce undesirable absorption in the film; and subsequently, modify the optical constants of the material during the ramp-up and stabilization period of the e-gun and ion-source, respectively. This paper characterizes the unwanted

  9. Searching for high-k RE2O3 nanoparticles embedded in SiO2 glass matrix

    NASA Astrophysics Data System (ADS)

    Mukherjee, S.; Lin, Y. H.; Kao, T. H.; Chou, C. C.; Yang, H. D.

    2012-03-01

    Significant experimental effort has been explored to search and characterize high-k materials with magnetodielectric effect (MDE) of series of rare earth (RE) oxide (RE2O3) nanoparticles (NPs) embedded in SiO2 glass matrix by a sol-gel route. Properly annealed sol-gel glass (in which RE = Sm, Gd, and Er) shows colossal response of dielectric constant along with diffuse phase transition and MDE around room temperature. The radial distribution functions, reconstructed from extended x-ray absorption fine structure, show the shortening of RE3 + -O depending on the RE2O3 NP size, which is consistent with oxygen vacancy induced dielectric anomaly. The magnetoresistive MDE is very much conditioned by magnetic property of RE2O3 NP grain, the degree of deformation of the lattice and constituent host.

  10. pH-Induced Release of Polyanions from Multilayer Films

    SciTech Connect

    Kharlampieva, Dr. Eugenia; Ankner, John Francis; Rubinstein, Michael; Sukhishvili, Prof. Svetlana A.

    2008-01-01

    We discovered pH-induced selective desorption and re-adsorption of weak polyacid chains from polyacid/polybase layer-by-layer films. In situ ATR-FTIR confirms the selectivity of polyacid release and shows that film response is caused by pH-induced charge imbalance. Experimentally, the characteristic time of chain release, τ, scales with molar mass, Mw, as Mw1.1 0.1. A new theoretical model of "sticky gel electrophoresis" of entangled polyacids agrees with experiments and predicts τ ~ Mw H, where H is film thickness. Neutron reflectivity shows that polyacid release results in disordering of the film structure.

  11. Temperature-sensitive hydrogels with SiO2-Au nanoshells for controlled drug delivery.

    PubMed

    Bikram, Malavosklish; Gobin, Andre M; Whitmire, Rachel E; West, Jennifer L

    2007-11-20

    Silica-gold (SiO(2)-Au) nanoshells are a new class of nanoparticles that consist of a silica dielectric core that is surrounded by a gold shell. These nanoshells are unique because their peak extinctions are very easily tunable over a wide range of wavelengths particularly in the near infrared (IR) region of the spectrum. Light in this region is transmitted through tissue with relatively little attenuation due to absorption. In addition, irradiation of SiO(2)-Au nanoshells at their peak extinction coefficient results in the conversion of light to heat energy that produces a local rise in temperature. Thus, to develop a photothermal modulated drug delivery system, we have fabricated nanoshell-composite hydrogels in which SiO(2)-Au nanoshells of varying concentrations have been embedded within temperature-sensitive hydrogels, for the purpose of initiating a temperature change with light. N-isopropylacrylamide-co-acrylamide (NIPAAm-co-AAm) hydrogels are temperature-sensitive hydrogels that were fabricated to exhibit a lower critical solution temperature (LCST) slightly above body temperature. The resulting composite hydrogels had the extinction spectrum of the SiO(2)-Au nanoshells in which the hydrogels collapsed reversibly in response to temperature (50 degrees C) and laser irradiation. The degree of collapse of the hydrogels was controlled by the laser fluence as well as the concentration of SiO(2)-Au nanoshells. Modulated drug delivery profiles for methylene blue, insulin, and lysozyme were achieved by irradiation of the drug-loaded nanoshell-composite hydrogels, which showed that drug release was dependent upon the molecular weight of the therapeutic molecule.

  12. A novel fabrication of a high performance SiO2-graphene oxide (GO) nanohybrids: Characterization of thermal properties of epoxy nanocomposites filled with SiO2-GO nanohybrids.

    PubMed

    Haeri, S Z; Ramezanzadeh, B; Asghari, M

    2017-05-01

    In this study it has been aimed to enhance the thermal resistance of epoxy coating through incorporation of SiO2-GO nanohybrids. SiO2-GO nanohybrids were synthesized through one-step sol-gel route using a mixture of Tetraethylorthosilane (TEOS) and 3-Aminopropyl triethoxysilane (APTES) silanes. The SiO2-GO nanohybrids were prepared at various hydrolysis times of 24, 48 and 72h. Then 0.2wt.% of GO and SiO2-GO nanohybrids were separately incorporated into the epoxy coating. Results revealed that amino functionalized SiO2 nanoparticles with particle size around 20-30nm successfully synthesized on the basal plane of GO. Results showed significant improvement of dispersion and interfacial interactions between nanohybrids and epoxy composite arising from covalent bonding between the SiO2-GO and the epoxy matrix. It was found that the thermal resistance of SiO2-GO nanohybrids and SiO2-GO/Epoxy nanocomposite was noticeably higher than GO and epoxy matrix, respectively.

  13. Whiter, brighter, and more stable cellulose paper coated with TiO2 /SiO2 core/shell nanoparticles using a layer-by-layer approach.

    PubMed

    Cheng, Fei; Lorch, Mark; Sajedin, Seyed Mani; Kelly, Stephen M; Kornherr, Andreas

    2013-08-01

    To inhibit the photocatalytic degradation of organic material supports induced by small titania (TiO2 ) nanoparticles, four kinds of TiO2 nanoparticles, that is, commercial P25-TiO2 , commercial rutile phase TiO2 , rutile TiO2 nanorods and rutile TiO2 spheres, prepared from TiCl4 , were coated with a thin, but dense, coating of silica (SiO2 ) using a conventional sol-gel technique to form TiO2 /SiO2 core/shell nanoparticles. These core/shell particles were deposited and fixed as a very thin coating onto the surface of cellulose paper samples by a wet-chemistry polyelectrolyte layer-by-layer approach. The TiO2 /SiO2 nanocoated paper samples exhibit higher whiteness and brightness and greater stability to UV-bleaching than comparable samples of blank paper. There are many potential applications for this green chemistry approach to protect cellulosic fibres from UV-bleaching in sunlight and to improve their whiteness and brightness.

  14. Functional photocatalytically active and scratch resistant antireflective coating based on TiO2 and SiO2

    NASA Astrophysics Data System (ADS)

    Mazur, M.; Wojcieszak, D.; Kaczmarek, D.; Domaradzki, J.; Song, S.; Gibson, D.; Placido, F.; Mazur, P.; Kalisz, M.; Poniedzialek, A.

    2016-09-01

    Antireflection (AR) multilayer coating, based on combination of five TiO2 and SiO2 thin films, was deposited by microwave assisted reactive magnetron sputtering process on microscope glass substrates. In this work X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy and wettability measurements were used to characterize the structural and surface properties of the deposited coating. These studies revealed that prepared coating was amorphous with low surface roughness. Photocatalytic properties were determined based on phenol decomposition reaction. Measurements of optical properties showed that transmittance in the visible wavelength range was increased after the deposition of AR coating as-compared to bare glass substrate. The mechanical properties were determined on the basis of nano-indentation and scratch resistance tests. Performed research has shown that deposition of an additional thin 10 nm thick TiO2 thin film top layer, the prepared AR coating was photocatalytically active, hydrophobic, scratch resistant and had increased hardness as-compared to bare glass substrate. These results indicate that prepared AR multilayer could be used also as a self-cleaning and protective coating.

  15. An ab initio investigation of Bi2Se3 topological insulator deposited on amorphous SiO2

    NASA Astrophysics Data System (ADS)

    de Oliveira, I. S. S.; Scopel, W. L.; Miwa, R. H.

    2017-02-01

    We use first-principles simulations to investigate the topological properties of Bi2Se3 thin films deposited on amorphous SiO2, Bi2Se3/a-SiO2, which is a promising substrate for topological insulator (TI) based device applications. The Bi2Se3 films are bonded to a-SiO2 mediated by van der Waals interactions. Upon interaction with the substrate, the Bi2Se3 topological surface and interface states remain present, however the degeneracy between the Dirac-like cones is broken. The energy separation between the two Dirac-like cones increases with the number of Bi2Se3 quintuple layers (QLs) deposited on the substrate. Such a degeneracy breaking is caused by (i) charge transfer from the TI to the substrate and charge redistribution along the Bi2Se3 QLs, and (ii) by deformation of the QL in contact with the a-SiO2 substrate. We also investigate the role played by oxygen vacancies ({{\\text{V}}\\text{O}} ) on the a-SiO2, which increases the energy splitting between the two Dirac-like cones. Finally, by mapping the electronic structure of Bi2Se3/a-SiO2, we found that the a-SiO2 surface states, even upon the presence of {{\\text{V}}\\text{O}} , play a minor role on gating the electronic transport properties of Bi2Se3.

  16. Improvement of low-humidity performance of PEMFC by addition of hydrophilic SiO 2 particles to catalyst layer

    NASA Astrophysics Data System (ADS)

    Jung, Un Ho; Park, Ki Tae; Park, Eun Hee; Kim, Sung Hyun

    Hydrophilic SiO 2 particles are added to the catalyst layer of a fuel cell membrane-electrode assembly (MEA) to improve wettability and performance at low-humidity conditions. The SiO 2 added MEAs are prepared by spraying technique and the contact angle is measured by the sessile drop method. The effects of SiO 2 additions of 0, 20, 40 and 60 wt.% (based on Pt/C) are investigated for various relative humidity levels in the anode and the cathode. The increased wettability of the cathode catalyst layer exerts an adverse effect on cell performance by causing flooding; this result demonstrates the hydrophilicity of SiO 2. With 40 wt.% addition of SiO 2 to the anode catalyst layer, the current density at 0.6 V and 0% relative humidity of the anode is 93% of that at 100% relative humidity. By comparison, the performance of a cell using a MEA with no added SiO 2 is only 85% of that at 0% relative humidity. A MEA with SiO 2 addition in the anode gives a higher performance at 60% relative humidity of the cathode than one with an undoped MEA. Increased wettability of the anode catalyst layer caused by SiO 2 addition renders it easy to absorb water from back diffusion.

  17. Influence of diamond wheel grinding process on surface micro-topography and properties of SiO2/SiO2 composite

    NASA Astrophysics Data System (ADS)

    Cao, Xiaoyan; Lin, Bin; Wang, Yan; Wang, Shaolei

    2014-02-01

    According to anisotropic and inhomogeneous structure of fiber-reinforced ceramic matrix composites (FRCMC), it is difficult to control the surface quality with the traditional method used in metal material. The present paper studies the influence of diamond wheel grinding process on surface micro-topography and properties of SiO2/SiO2 composite. The research is based on some new discovery that the material enhanced fiber orientations play a key role in micro-topography of FRCMC grinding surface. Through a series of experiments, we investigate the relationship between grinding process and the quality of composites surface. We also analyze characteristics of the material surface topography height, wave distribution and surface support properties in details. This paper employs the orthogonal design to optimize grinding process parameters and also successfully models a critical condition to modify the surface characteristics. The results show that speed of grinding wheel has the greatest influence on height and surface support properties, the next is grain mesh size and depth of cut. The grain mesh size is the key factor for surface micro-topography modification. Compared to the surface with woven texture, the modified surface has better symmetrical characteristic. The research obtained will be an important technical support on improving the processing quality of FRCMC.

  18. Optimization of the optical properties of Er-doped Si-rich SiO 2/SiO 2 multilayers obtained by reactive magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Gourbilleau, F.; Dufour, C.; Madelon, R.; Rizk, R.

    2006-05-01

    The effects of annealing time and of Si nanocluster (Si-nc) size on the coupling rate to Er ions were investigated through studies made on multilayers (MLs) consisting in about 20 periods of Er-doped Si-rich SiO 2/SiO 2. These MLs were deposited by reactive magnetron sputtering at 650 °C and subsequently annealed at 900 °C. A steep increase of the PL emission is observed for short annealing time while a trend of some saturation occurs for longer treatment time. Besides, the Er lifetime continuously increases with the annealing time. For Si-rich layer thickness or Si-nc larger than about 5 nm, the rate of energy transfer is lowered because of the weak confinement of carriers and the loss of resonant excitation of Er through the upper levels (second, third, etc.). The latter is liable to prevent the energy back transfer process, while the weak confinement reduces strongly the probability of no phonon radiative recombination that governs the transfer excitation rate from Si-nc to Er ions.

  19. Surface-induced solid-liquid phase transitions in ultra-thin water films at T > 0 ^oC

    NASA Astrophysics Data System (ADS)

    Chakraborty, Animesh; Gellman, Andrew; Baker, Layton; Broitman, Estebahn

    2008-03-01

    We report here the measurements of both the adsorption isotherms and the dissipation in ultra-thin films of water adsorbed on the surfaces of SiO2 . The measurements were made in a small high vacuum chamber in which we have mounted a QCM. The chamber was evacuated to ˜10-8 Torr and then filled with water vapor at pressures ranging from 10-3 -- 40 Torr (the vapor pressure of water at room temperature is ˜22 Torr). In addition the temperature of the apparatus can be varied in the range 10 -- 60^oC. This is sufficient to measure the adsorption isotherm and to probe the phase of adsorbed water films over the range of conditions. Recently published work studying the adsorption of water on the SiO2 layer formed on Si single crystals has suggested that the phase of the water at temperatures well above 0^oC is actually that of a solid, ice-like structure rather than liquid water [1]. That work is based on the comparison of the vibrational spectrum of thin water films with those of liquid water and ice. In our study we are using the QCM to investigate the possibility of formation of Ice-like structures on SiO2. [1] Asay, D. B. and Kim, S.H., Evolution of the Adsorbed Water Layer Structure on Silicon Oxide at Room Temperature. J. Phys. Chem. B. 2005, 109, 16760-16763

  20. Laser-induced vibration of a thin soap film.

    PubMed

    Emile, Olivier; Emile, Janine

    2014-09-21

    We report on the vibration of a thin soap film based on the optical radiation pressure force. The modulated low power laser induces a counter gravity flow in a vertical free-standing draining film. The thickness of the soap film is then higher in the upper region than in the lower region of the film. Moreover, the lifetime of the film is dramatically increased by a factor of 2. Since the laser beam only acts mechanically on the film interfaces, such a film can be employed in an optofluidic diaphragm pump, the interfaces behaving like a vibrating membrane and the liquid in-between being the fluid to be pumped. Such a pump could then be used in delicate micro-equipment, in chips where temperature variations are detrimental and even in biological systems.

  1. Structural characterization and oxidative dehydrogenation activity of V2O5/Ce(x)Zr(1-x)O2/SiO2 catalysts.

    PubMed

    Reddy, Benjaram M; Lakshmanan, Pandian; Loridant, Stéphane; Yamada, Yusuke; Kobayashi, Tetsuhiko; López-Cartes, Carlos; Rojas, Teresa C; Fernandez, Asunción

    2006-05-11

    The thermal stability of a nanosized Ce(x)Zr(1-x)O2 solid solution on a silica surface and the dispersion behavior of V2O5 over Ce(x)Zr(1-x)O2/SiO2 have been investigated using XRD, Raman spectroscopy, XPS, HREM, and BET surface area techniques. Oxidative dehydrogenation of ethylbenzene to styrene was performed as a test reaction to assess the usefulness of the VOx/Ce(x)Zr(1-x)O2/SiO2 catalyst. Ce(x)Zr(1-x)O2/SiO2 (1:1:2 mol ratio based on oxides) was synthesized through a soft-chemical route from ultrahigh dilute solutions by adopting a deposition coprecipitation technique. A theoretical monolayer equivalent to 10 wt % V2O5 was impregnated over the calcined Ce(x)Zr(1-x)O2/SiO2 sample (773 K) by an aqueous wet impregnation technique. The prepared V2O5/Ce(x)Zr(1-x)O2/SiO2 sample was subjected to thermal treatments from 773 to 1073 K. The XRD measurements indicate the presence of cubic Ce0.75Zr0.25O2 in the case of Ce(x)Zr(1-x)O2/SiO2, while cubic Ce0.5Zr0.5O2 and tetragonal Ce0.16Zr0.84O2 in the case of V2O5/Ce(x)Zr(1-x)O2/SiO2 when calcined at various temperatures. Dispersed vanadium oxide induces more incorporation of zirconium into the ceria lattice, thereby decreasing its lattice size and also accelerating the crystallization of Ce-Zr-O solid solutions at higher calcination temperatures. Further, it interacts selectively with the ceria portion of the composite oxide to form CeVO4. The RS measurements provide good evidence about the dispersed form of vanadium oxide and the CeVO4 compound. The HREM studies show the presence of small Ce-Zr-oxide particles of approximately 5 nm size over the surface of amorphous silica and corroborate with the results obtained from other techniques. The catalytic activity studies reveal the ability of vanadium oxide supported on Ce(x)Zr(1-x)O2/SiO2 to efficiently catalyze the ODH of ethylbenzene at normal atmospheric pressure. The remarkable ability of Ce(x)Zr(1-x)O2 to prevent the deactivation of supported vanadium oxide leading to

  2. SiO2/polyacrylonitrile membranes via centrifugal spinning as a separator for Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Yanilmaz, Meltem; Lu, Yao; Li, Ying; Zhang, Xiangwu

    2015-01-01

    Centrifugal spinning is a fast, cost-effective and safe alternative to the electrospinning technique, which is commonly used for making fiber-based separator membranes. In this work, SiO2/polyacrylonitrile (PAN) membranes were produced by using centrifugal spinning and they were characterized by using different electrochemical techniques for use as separators in Li-ion batteries. SiO2/PAN membranes exhibited good wettability and high ionic conductivity due to their highly porous fibrous structure. Compared with commercial microporous polyolefin membranes, SiO2/PAN membranes had larger liquid electrolyte uptake, higher electrochemical oxidation limit, and lower interfacial resistance with lithium. SiO2/PAN membrane separators were assembled into lithium/lithium iron phosphate cells and these cells delivered high capacities and exhibited good cycling performance at room temperature. In addition, cells using SiO2/PAN membranes showed superior C-rate performance compared to those using microporous PP membrane.

  3. Effect of nano SiO2 particles on the morphology and mechanical properties of POSS nanocomposite dental resins

    NASA Astrophysics Data System (ADS)

    Liu, Yizhi; Sun, Yi; Zeng, Fanlin; Xie, Weili; Liu, Yang; Geng, Lin

    2014-12-01

    Nanocomposite dental resins composed of polyhedral oligomeric silsesquioxane nanocomposite matrix and 0, 0.5,1, 1.5 and 2 wt% nano SiO2 as filler were prepared by light curing method. The nanocomposite resins were characterized by performing compressive, three-point flexure, nanoindentation and nanoscratch testings as well as optical microscopy and scanning electron microscope analysis. The effects of different nano SiO2 contents were studied on compressive strength, flexural strength, hardness and resistance of composite resin. From the mechanical results, it was found that nano SiO2 effectively enhanced the mechanical properties of the composite resins at low content. With the increase of the nano SiO2 content, the mechanical properties decreased. It was attributed to the content of nano SiO2 and dispersion of nanoparticles in matrix.

  4. Fabrication of ordered poly(methyl methacrylate) nanobowl arrays using SiO2 colloidal crystal templates.

    PubMed

    Deng, Lier; Fu, Ming; Tao, Yinglei; Guo, Xiaoyun

    2014-06-01

    A simple approach is presented for the fabrication of poly(methyl methacrylate) (PMMA) nanobowl arrays over cm2 areas using SiO2 colloidal crystal templates. SiO2 colloidal crystal templates were prepared on a clean glass substrate by self-assembled SiO2 spheres of 410 nm in diameter. The air between the silica spheres was filled by the superfluous monomer of PMMA that can be subsequently polymerized. After infiltration, the SiO2-PMMA templates were immersed in a 3 wt% hydrofluoric acid (HF) aqueous solution. After 24 h, silica spheres were etched and a free-standing nanobowl sheet was obtained. The size of the nanobowls could be controlled by the size of the SiO2 spheres and the area of the nanobowl sheet could be altered by the size of the glass substrate.

  5. ZnO:Mo:In nanofilms on SiO2 substrate under investigation framework of the second optical transition

    NASA Astrophysics Data System (ADS)

    Souissi, A.; Amlouk, M.; Guermazi, S.

    2017-02-01

    ZnO and ZnO:Mo:In nanofilms were deposited on SiO2 substrate at 460 °C by the spray pyrolysis method with the molar ratio (Mo/Zn) set at 1% and (In/Zn) dosed at 1%, 2%, 3% and 10%. The optical, dielectric and photonic characteristics of these samples were analyzed from the optical spectra of transmission and reflection, which revealed the presence of two absorption edges. The first one was related to the ZnO:Mo:In typical transition and the second edge originated from the ZnO:Mo:In/SiO2 interface transition by the probable formation of an ultrafine layer identified as SiOx and/or ZnO(1-x)SiO2(x). The optical gap and Urbach energies of ZnO:Mo:In nanofilms varied almost uniformly and in a complementary manner depending on the co-doping of ∼3.28-3.24 eV and ∼82-136 meV. These energies associated with the interface varied randomly from 3.93 to 4.18 eV and ∼263 to 408 meV, and showed strong dependencies with the structural, crystalline and vibrational properties previously studied. They also displayed possible correlations with electron scattering time and the dc photoconductivity which reaches high value for film prepared using In = 2%. AFM study showed variable morphologies of the surfaces that are responsive to codoping elements, therefore at the interface, wherein the film growth began. All these factors influenced the results described above. The study also showed good agreement between rms roughness and TC texture coefficient of the studied films, of high transparency ∼89-92%. The films prepared with In = 2% revealed a high photoconductivity and could be used in photocatalytic and photonic applications.

  6. Bacterial cellulose composites loaded with SiO2 nanoparticles: Dynamic-mechanical and thermal properties.

    PubMed

    Sheykhnazari, Somayeh; Tabarsa, Taghi; Ashori, Alireza; Ghanbari, Abbas

    2016-12-01

    The aim of this paper was to prepare composites of bacterial cellulose (BC) filled with silica (SiO2) nanoparticles to evaluate the influence of the SiO2 contents (3, 5 and 7wt%) on the thermo-mechanical properties of the composites. BC hydro-gel was immersed in an aqueous solution of silanol derived from tetraethoxysilane (TEOS), the silanol was then converted into SiO2 in the BC matrix by pressing at 120°C and 2MPa. The BC/SiO2 translucent sheets were examined by dynamic-mechanical analysis (DMA), thermo gravimetric analysis (TGA), and scanning electron microscopy (SEM). The temperature dependence of the storage modulus, loss modulus and tan delta was determined by DMA. In general, the results revealed that the increment of storage modulus and thermal stability increased concomitantly with the augmentation of SiO2 content. Therefore, it could be concluded that the mechanical properties of the composites were improved by using high amounts of nano silica. This would be a high aspect ratio of BC capable of connecting the BC matrix and SiO2, thereby enhancing a large contact surface and resulting in excellent coherence. A decrease of the storage modulus was consistent with increasing temperature, resulting from softening of the composites. The storage modulus of the composites increased in the order: BC/S7>BC/S5>BC/S3, while the loss modulus and tan delta decreased. On the other hand, the thermal stabilities of all BC/SiO2 composites were remarkably enhanced as compared to the pristine BC. TGA curves showed that the temperature of decomposition of the pure BC gradually shifted from about 260°C to about 370°C as silica content increased. SEM observations illustrated that the nano-scale SiO2 was embedded between the voids and nano-fibrils of the BC matrix. Overall, the results indicated that the successful synthesis and superior properties of BC/SiO2 advocate its effectiveness for various applications.

  7. Physiological responses induced by emotion-eliciting films.

    PubMed

    Fernández, Cristina; Pascual, Juan C; Soler, Joaquim; Elices, Matilde; Portella, Maria J; Fernández-Abascal, Enrique

    2012-06-01

    Emotion-eliciting films are commonly used to evoke subjective emotional responses in experimental settings. The main aim of the present study was to investigate whether a set of film clips with discrete emotions were capable to elicit measurable objective physiological responses. The convergence between subjective and objective measures was evaluated. Finally, the effect of gender on emotional responses was investigated. A sample of 123 subjects participated in the study. Individuals were asked to view a set of emotional film clips capable to induce seven emotions: anger, fear, sadness, disgust, amusement, tenderness and neutral state. Skin conductance level (SCL), heart rate (HR) and subjective emotional responses were measured for each film clip. In comparison with neutral films, SCL was significantly increased after viewing fear films, and HR was also significantly incremented for anger and fear films. Physiological variations were associated with arousal measures indicating a convergence between subjective and objective reactions. Women appeared to display significantly greater SCL and HR responses for films inducing sadness. The findings suggest that physiological activation would be more easily induced by emotion-eliciting films that tap into emotions with higher subjective arousal such as anger and fear.

  8. Fabrication of multifunctional SiO2@GN-serum composites for chemo-photothermal synergistic therapy.

    PubMed

    Liu, Yuwei; Bai, Jing; Jia, Xiaodan; Jiang, Xiue; Guo, Zhuo

    2015-01-14

    Recently, the chemo-photothermal synergistic therapy has become a potential method for cancer treatment. Herein, we developed a multifunctional nanomaterial for chemo-photothermal therapeutics based on silica and graphene core/shell structure (SiO2@GN) because of the ability of GN to convert light energy into heat. Serum protein was further modified onto the surface of GN (SiO2@GN-Serum) to improve the solubility and stability of GN-based nanoparticles in physiological conditions. The as-synthesized SiO2@GN-Serum nanoparticles (NPs) have been revealed to have high photothermal conversion efficiency and stability, as well as high storage and release capacity for anticancer drug doxorubicin (SiO2@GN-Serum-Dox). The therapeutic efficacy of SiO2@GN-Serum-Dox has been evaluated in vitro and in vivo for cervical cancer therapy. In vitro cytotoxicity tests demonstrate that SiO2@GN-Serum NPs have excellent biocompatibility. However, SiO2@GN-Serum-Dox NPs show higher cytotoxicity than SiO2@GN-Serum and free Dox under irradiation with NIR laser at 1.0 W/cm(2) for 5 min owing to both SiO2@GN-Serum-mediated photothermal ablation and cytotoxicity of light-triggered Dox release. In mouse models, the tumor growth is significantly inhibited by chem-photothermal effect of SiO2@GN-Serum-Dox. Overall, compared with single chemotherapy or photothermal therapy, the combined treatment demonstrates better therapeutic efficacy. Our results suggest a promising GN-based core/shell nanostructure for biomedical applications.

  9. Investigations of Surface Reactions in Neutral Loop Discharge Plasma for High-Aspect-Ratio SiO2 Etching

    NASA Astrophysics Data System (ADS)

    Morikawa, Yasuhiro; Chen, Wei; Hayashi, Toshio; Uchida, Taijiro

    2003-03-01

    The relationship between fine etching and gas structure in magnetic neutral loop discharge (NLD) plasma has been investigated using C4F8, C3F8, and CF3FOC=CF2 (HFE-216) gases. It was found that CF3+ ions were effectively generated in the HFE-216 plasma compared with those in the C4F8 or C3F8 plasma under the same conditions. Hydrofluorocarbon (HFC) gases such as CH2F2 (HFC-32) and CH3CHF2 (HFC-152a) were also employed to realize highly selective etching for SiO2 to the photoresist. C1s X-ray photoelectron spectra showed a prevalence of C-C and C-CFx bonds in the films deposited on the surface in the HFC plasma. This implies that the deposited film was mainly composed of carbon atoms. It was also found from X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared (FTIR) analyses that the chemical state of fluorine in this film was not C-F, but H-C-F. This may lead to the realization of microloading free etching with high resist selectivity in the HFE-216/HFC-152a mixture plasma. Studies on the relationship between etch performance and thin H-C-F polymer film formation were carried out in the HFE-216/HFC-152a mixture plasma. It can be thought that the interaction of the H-C-F film on the surface and CxFy species from the plasma is very low compared with that of a C-F film. The H-C-F film on the sidewall may play serve as a lubricant and may transport etchants to the bottom of the etched pattern. As a result, 50-nm-diameter holes and 40 nm space patterns with aspect ratios of 18 and 22.5, respectively, were successfully fabricated in the HFE-216 + HFC-152a + O2 plasma. The H-C-F film formation on the etched surface enables high-aspect-ratio etching with high selectivity.

  10. Induced electronic anisotropy in bismuth thin films

    SciTech Connect

    Liao, Albert D.; Yao, Mengliang; Opeil, Cyril; Katmis, Ferhat; Moodera, Jagadeesh S.; Li, Mingda; Tang, Shuang; Dresselhaus, Mildred S.

    2014-08-11

    We use magneto-resistance measurements to investigate the effect of texturing in polycrystalline bismuth thin films. Electrical current in bismuth films with texturing such that all grains are oriented with the trigonal axis normal to the film plane is found to flow in an isotropic manner. By contrast, bismuth films with no texture such that not all grains have the same crystallographic orientation exhibit anisotropic current flow, giving rise to preferential current flow pathways in each grain depending on its orientation. Extraction of the mobility and the phase coherence length in both types of films indicates that carrier scattering is not responsible for the observed anisotropic conduction. Evidence from control experiments on antimony thin films suggests that the anisotropy is a result of bismuth's large electron effective mass anisotropy.

  11. Carrier dynamics in Si nanocrystals in an SiO2 matrix investigated by transient light absorption

    NASA Astrophysics Data System (ADS)

    de Boer, W. D. A. M.; de Jong, E. M. L. D.; Timmerman, D.; Gregorkiewicz, T.; Zhang, H.; Buma, W. J.; Poddubny, A. N.; Prokofiev, A. A.; Yassievich, I. N.

    2013-10-01

    We report on investigations of optical carrier generation in silicon nanocrystals embedded in an SiO2 matrix. Carrier relaxation and recombination processes are monitored by means of time-resolved induced absorption, using a conventional femtosecond pump-probe setup for samples containing different average sizes of nanocrystals (dNC = 2.5-5.5 nm). The electron-hole pairs generated by the pump pulse are probed by a second pulse over a broad spectral range (Eprobe = 0.95-1.35 or 1.6-3.25 eV), by which information on excited states is obtained. Under the same excitation conditions, we observe that the induced absorption intensity in the near-infrared range is a factor of ˜10 higher than in the visible range. To account for these observations, we model the spectral dependence of the induced absorption signal using an empirical sp3d5s* tight-binding technique, by which the spectrum can be well reproduced up to a certain threshold. For probe photon energies above this threshold (dependent on nanocrystal size), the induced absorption signal is found to feature a long-standing component, whereas the induced absorption signal for probe photon energies below this value vanishes within 0.5 ns. We explain this by self-trapping of excitons on surface-related states.

  12. Fluorocarbon assisted atomic layer etching of SiO2 and Si using cyclic Ar/C4F8 and Ar/CHF3 plasma

    DOE PAGES

    Metzler, Dominik; Li, Chen; Engelmann, Sebastian; ...

    2015-11-11

    The need for atomic layer etching (ALE) is steadily increasing as smaller critical dimensions and pitches are required in device patterning. A flux-control based cyclic Ar/C4F8 ALE based on steady-state Ar plasma in conjunction with periodic, precise C4F8 injection and synchronized plasma-based low energy Ar+ ion bombardment has been established for SiO2.1 In this work, the cyclic process is further characterized and extended to ALE of silicon under similar process conditions. The use of CHF3 as a precursor is examined and compared to C4F8. CHF3 is shown to enable selective SiO2/Si etching using a fluorocarbon (FC) film build up. Othermore » critical process parameters investigated are the FC film thickness deposited per cycle, the ion energy, and the etch step length. Etching behavior and mechanisms are studied using in situ real time ellipsometry and X-ray photoelectron spectroscopy. Silicon ALE shows less self-limitation than silicon oxide due to higher physical sputtering rates for the maximum ion energies used in this work, ranged from 20 to 30 eV. The surface chemistry is found to contain fluorinated silicon oxide during the etching of silicon. As a result, plasma parameters during ALE are studied using a Langmuir probe and establish the impact of precursor addition on plasma properties.« less

  13. Antibacterial activity of large-area monolayer graphene film manipulated by charge transfer.

    PubMed

    Li, Jinhua; Wang, Gang; Zhu, Hongqin; Zhang, Miao; Zheng, Xiaohu; Di, Zengfeng; Liu, Xuanyong; Wang, Xi

    2014-03-12

    Graphene has attracted increasing attention for potential applications in biotechnology due to its excellent electronic property and biocompatibility. Here we use both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) to investigate the antibacterial actions of large-area monolayer graphene film on conductor Cu, semiconductor Ge and insulator SiO2. The results show that the graphene films on Cu and Ge can surprisingly inhibit the growth of both bacteria, especially the former. However, the proliferation of both bacteria cannot be significantly restricted by the graphene film on SiO2. The morphology of S. aureus and E. coli on graphene films further confirms that the direct contact of both bacteria with graphene on Cu and Ge can cause membrane damage and destroy membrane integrity, while no evident membrane destruction is induced by graphene on SiO2. From the viewpoint of charge transfer, a plausible mechanism is proposed here to explain this phenomenon. This study may provide new insights for the better understanding of antibacterial actions of graphene film and for the better designing of graphene-based antibiotics or other biomedical applications.

  14. Microwave absorption properties and mechanism of cagelike ZnO /SiO2 nanocomposites

    NASA Astrophysics Data System (ADS)

    Cao, Mao-Sheng; Shi, Xiao-Ling; Fang, Xiao-Yong; Jin, Hai-Bo; Hou, Zhi-Ling; Zhou, Wei; Chen, Yu-Jin

    2007-11-01

    In this paper, cagelike ZnO /SiO2 nanocomposites were prepared and their microwave absorption properties were investigated in detail. Dielectric constants and losses of the pure cagelike ZnO nanostructures were measured in a frequency range of 8.2-12.4GHz. The measured results indicate that the cagelike ZnO nanostructures are low-loss material for microwave absorption in X band. However, the cagelike ZnO /SiO2 nanocomposites exhibit a relatively strong attenuation to microwave in X band. Such strong absorption is related to the unique geometrical morphology of the cagelike ZnO nanostructures in the composites. The microcurrent network can be produced in the cagelike ZnO nanostructures, which contributes to the conductive loss.

  15. The growth and in situ characterization of chemical vapor deposited SiO2

    NASA Technical Reports Server (NTRS)

    Iyer, R.; Chang, R. R.; Lile, D. L.

    1987-01-01

    This paper reports the results of studies of the kinetics of remote (indirect) plasma enhanced low pressure CVD growth of SiO2 on Si and InP and of the in situ characterization of the electrical surface properties of InP during CVD processing. In the latter case photoluminescence was employed as a convenient and sensitive noninvasive method for characterizing surface trap densities. It was determined that, provided certain precautions are taken, the growth of SiO2 occurs in a reproducible and systematic fashion that can be expressed in an analytic form useful for growth rate prediction. Moreover, the in situ photoluminescence studies have yielded information on sample degradation resulting from heating and chemical exposure during the CVD growth.

  16. Products of hydratation in fine grained mixtures MgO - SiO2

    NASA Astrophysics Data System (ADS)

    Szczerba, J.; Prorok, R.; Madej, D.; Sniezek, E.

    2013-12-01

    The aim of this study was to evaluate the influence of time of ageing on phase evolution of paste from MgO-SiO2-H2O phase system. The paste was composed of fine grained sintered magnesia and microsilica in 1:2 molar ratio and water, with water to solid ratio equal 0,5. After preparation the paste was ageing during specified time up to 180 days in temperature 20° C. Phase composition of mixture of MgO and SiO2 with water was studied by XRD, DTA-TGA. The analysis revealed that product of reaction in mixture of MgO, SiO2 and water was a probably poorly crystalline magnesium silicate.

  17. Temperature-dependent defect dynamics in the network glass SiO2

    NASA Astrophysics Data System (ADS)

    Vollmayr-Lee, Katharina; Zippelius, Annette

    2013-11-01

    We investigate the long time dynamics of a strong glass former, SiO2, below the glass transition temperature by averaging single-particle trajectories over time windows which comprise roughly 100 particle oscillations. The structure on this coarse-grained time scale is very well defined in terms of coordination numbers, allowing us to identify ill-coordinated atoms, which are called defects in the following. The most numerous defects are O-O neighbors, whose lifetimes are comparable to the equilibration time at low temperature. On the other hand, SiO and OSi defects are very rare and short lived. The lifetime of defects is found to be strongly temperature dependent, consistent with activated processes. Single-particle jumps give rise to local structural rearrangements. We show that in SiO2 these structural rearrangements are coupled to the creation or annihilation of defects, giving rise to very strong correlations of jumping atoms and defects.

  18. Anisotropy of selective epitaxy in nanoscale-patterned growth: GaAs nanowires selectively grown on a SiO2-patterned (001) substrate by molecular-beam epitaxy

    NASA Astrophysics Data System (ADS)

    Lee, S. C.; Dawson, L. R.; Brueck, S. R. J.; Jiang, Y.-B.

    2005-12-01

    Anisotropic selective epitaxy in nanoscale-patterned growth (NPG) by molecular-beam epitaxy is investigated on a 355nm period two-dimensional array of circular holes fabricated in a 30-nm-thick SiO2 film on a GaAs(001) substrate. The hole diameter ranged from 70to150nm. The small hole diameter and the very thin masking layer stimulated lateral growth over the SiO2 surface at an early stage of selective epitaxy on this patterned substrate. Lateral overgrowth associated with selective epitaxy, however, did not proceed isotropically along the circular boundary between the open substrate surface and the SiO2 mask. There was preferential growth direction parallel to ⟨111⟩B. This anisotropy in the selective epitaxy resulted in the formation of a nanoscale, nontapered, straight-wire-type epitaxial layer (GaAs nanowires), which had a length of up to 1.8μm for a nominal 200nm deposition. Every GaAs nanowire had a hexagonal prismatic shape directed along ⟨111⟩B and was surrounded by six (110) sidewalls. The anisotropy of selective epitaxy and faceting in NPG were affected by the profile of the SiO2 mask and are interpreted using a minimization of the total surface energy for equilibrium crystal shape.

  19. First-principles study of the threshold effect in the electronic stopping power of LiF and SiO2 for low-velocity protons and helium ions

    NASA Astrophysics Data System (ADS)

    Mao, Fei; Zhang, Chao; Dai, Jinxia; Zhang, Feng-Shou

    2014-02-01

    Nonadiabatic dynamics simulations are performed to investigate the electronic stopping power of LiF and SiO2-cristobalite-high crystalline thin films when protons and helium ions are hyperchanneling in the <001> axis. In this theoretical framework, ab initio time-dependent density-functional theory calculations for electrons are combined with molecular dynamics simulations for ions in real time and real space. The energy transfer process between the ions and the electronic subsystem of LiF and SiO2 nanostructures is studied. The velocity-proportional stopping power of LiF and SiO2 for protons and helium ions is predicted in the low-energy range. The measured velocity thresholds of protons in LiF and SiO2, and helium ions in LiF are reproduced. The convergence of the threshold effect with respect to the separation of grid points is confirmed. The underlying physics of the threshold effect is clarified by analyzing the conduction band electron distribution. In addition, the electron transfer processes between the projectile ions and solid atoms in hyperchanneling condition are studied, and its effects on the energy loss is investigated.

  20. Preparation of xerogel SiO2 from roasted iron sand under various acidic solution

    NASA Astrophysics Data System (ADS)

    Ramelan, A. H.; Wahyuningsih, S.; Ismoyo, Y. A.; Pranata, H. P.; Munawaroh, H.

    2016-11-01

    Xerogel SiO2 had been prepared from roasted iron sand through variation of Na2CO3 addition and sol-gel process under various acidic solution. Roasting treatment was carried out on the compositional variation of iron sand:Na2CO3 = 1:2; 1:1 and 2:1 at 1100 °C. While the sol-gel process was conducted at room temperature and neutralized using HCl 0.1 M and 6 M. The color characteristics of roasted iron sand shown light brown, dark brown and dark gray of the compositional variation of iron sand:Na2CO3 = 1:2; 1:1 and 2:1, respectively. In addition, the levels of thoughness increased by increasing the ratio of sand in the composition of the mixture. The best composition of roasted treatment was at a variety of iron sand:Na2SiO3 = 1:2 with 57.72% had been dissolved in hot water. The addition of Na2CO3 will influence the Na2SiO3 formation, because of the increase of Na2CO3 capable produced the iron sand decomposition product. Na2SiO3 gel had been produced after it was neutralized with certain amount of HCl solution. The neutralization was more effective if using high concentration of HCl because of the formation of gel SiO2 will be easier occurred. The results of SiO2 had been identified by the FTIR spectra, which an absorption spectra of Si-O-Si asymmetric stretching at 1098.51 cm-1, symmetric stretching of Si-O-Si at 804.35 cm-1 and the bending O-Si-O at 469.69 cm'1. The result of SiO2 content by XRF analysis is about 85.15%.

  1. Precautions toward XTEM of Si3N4/SiO2

    NASA Technical Reports Server (NTRS)

    Ogbuji, Linus U. J. T.

    1991-01-01

    Severe difficulties are encountered in the preparation of oxidized Si3N4 specimens for XTEM transmission electromicroscopic inspection, in virtue of the extreme difference between Si3N4 and SiO2 mechanical properties. Attention is presently given to a preparation method in which an overlayer of the nitride is always occluded; this protects the oxide through most of the thinning that specimen preparation entails. An XTEM image of the oxide/nitride interface is presented.

  2. Morphology, Microstructure and Transport Properties of ZnO Decorated SiO2 Nanoparticles (Preprint)

    DTIC Science & Technology

    2010-04-15

    INTRODUCTION One dimensional nanostructures such as nanowires, nanotubes, and nanoshells have received a great deal of interest because of their morphology...nanoparticles were resuspended. This washing process was repeated three times. In the hydrolytic ZnO synthesis method, a 1 ml suspension of SiO2 nanoshells in...Brownian motion and relates this to the size of the particles being measured. An important feature of Brownian motion measured by DLS is that small particles

  3. Measurements of SiO2 glass surface parameters by methods of microscopy

    NASA Astrophysics Data System (ADS)

    Gavars, Eduards; Svagere, Anda; Skudra, Atis; Zorina, Natalia; Poplausks, Raimonds

    2012-08-01

    In this research we compare chemical and plasma treatment methods for surface of SiO2 glass. For chemical treatment of surface tequila and alcohol were used but for plasma treatment - Ar+As and Ar+Se plasmas. Surface topography was analyzed using atomic force microscope. Comparison of chemical and plasma treatment methods shows that surface treated with plasma is smoother. Because of their various chemical compositions tequila and alcohol show different results.

  4. SEGR in SiO$${}_2$$ –Si$$_3$$ N$$_4$$ Stacks

    DOE PAGES

    Javanainen, Arto; Ferlet-Cavrois, Veronique; Bosser, Alexandre; ...

    2014-04-17

    This work presents experimental SEGR data for MOS-devices, where the gate dielectrics are are made of stacked SiO2–Si3N4 structures. Also a semi-empirical model for predicting the critical gate voltage in these structures under heavy-ion exposure is proposed. Then statistical interrelationship between SEGR cross-section data and simulated energy deposition probabilities in thin dielectric layers is discussed.

  5. Optical and other material properties of SiO2 from ab initio studies

    NASA Astrophysics Data System (ADS)

    Warmbier, Robert; Mohammed, Faris; Quandt, Alexander

    2014-07-01

    The optical properties of photonic devices largely depend on the dielectric properties of the underlying materials. We apply modern ab initio methods to study crystalline SiO2 phases, which serve as toy models for amorphous glass. We discuss the dielectric response from the infrared to the VIS/UV, which is crucial for glass based photonic applications. Low density silica, like cristobalite, may provide a good basis for high transmission optical devices.

  6. A highly efficient g-C3N4/SiO2 heterojunction: the role of SiO2 in the enhancement of visible light photocatalytic activity.

    PubMed

    Hao, Qiang; Niu, Xiuxiu; Nie, Changshun; Hao, Simeng; Zou, Wei; Ge, Jiangman; Chen, Daimei; Yao, Wenqing

    2016-11-23

    SiO2, an insulator, hardly has any photocatalytic acitivity due to its intrinsic property, and it is generally used as a hard template to increase the surface area of catalysts. However, in this work, we found that the surface state of the insulator SiO2 can promote the migration of photogenerated charge carriers, leading to the enhancement of the photooxidation ability of graphitic carbon nitride (g-C3N4). A one-pot calcination method was employed to prepare g-C3N4/SiO2 composites using melamine and SiO2 as precursors. The composites present considerably high photocatalytic degradation activities for 2,4-dichlorophenol (2,4-DCP) and rhodamine B (RhB) under visible light (λ > 420 nm) irradiation, which are about 1.53 and 4.18 times as high as those of bulk g-C3N4, respectively. The enhancement of the photocatalytic activity is due to the fact that the introduction of the insulator SiO2 in g-C3N4/SiO2 composites can greatly improve the specific surface area of the composites; more importantly, the impurity energy level of SiO2 can help accelerate the separation and transfer of electron-hole pairs of g-C3N4. Electron paramagnetic resonance (EPR) spectroscopy and trapping experiments with different radical scavengers show that the main active species of g-C3N4 are superoxide radicals, while holes also play a role in photodegradation. For g-C3N4/SiO2-5, besides superoxide radicals and holes, the effect of hydroxyl radicals was greatly improved. Finally, a possible mechanism for the photogenerated charge carrier migration of the g-C3N4/SiO2 photocatalyst was proposed.

  7. Synthesis and characterization of Fe3O4-SiO2-AgCl photocatalyst

    NASA Astrophysics Data System (ADS)

    Husni, H. N.; Mahmed, N.; Ngee, H. L.

    2016-07-01

    Magnetite-silica-silver chloride (Fe3O4-SiO2-AgCl) coreshell particles with AgCl crystallite size of 117 nm was prepared by a wet chemistry method at ambient temperature. The magnetite-core was synthesized by using iron (II) sulfate heptahydrate (FeSO4•7H2O) and iron (III) sulfate hydrate (Fe2(SO4)3) with ammonium hydroxide (NH4OH) as the precipitating agent. The silica-shell was synthesized by using a modified Stöber process. The silver ions (Ag+) was adsorbed onto the silica surface after Söber process, followed by the addition of Cl- and polyvinylpyrrolidone (PVP) for the formation of Fe3O4-SiO2-AgCl coreshell particles. The effectiveness of the synthesized photocatalyst was investigated by monitoring the degradation of the methylene blue (MB) under sunlight for five cycles. About 90 % of the MB solution can be degraded after 2 hours. The degradation of MB solution by the Fe3O4-SiO2-AgCl particles is highly efficient for first three cycles according to the MB concentration recorded by the UV-Visible spectroscopy (UV-Vis). Nevertheless, the synthesized particles could be a promising material for photocatalytic applications.

  8. Strong piezoelectricity in single-layer graphene deposited on SiO2 grating substrates.

    PubMed

    da Cunha Rodrigues, Gonçalo; Zelenovskiy, Pavel; Romanyuk, Konstantin; Luchkin, Sergey; Kopelevich, Yakov; Kholkin, Andrei

    2015-06-25

    Electromechanical response of materials is a key property for various applications ranging from actuators to sophisticated nanoelectromechanical systems. Here electromechanical properties of the single-layer graphene transferred onto SiO2 calibration grating substrates is studied via piezoresponse force microscopy and confocal Raman spectroscopy. The correlation of mechanical strains in graphene layer with the substrate morphology is established via Raman mapping. Apparent vertical piezoresponse from the single-layer graphene supported by underlying SiO2 structure is observed by piezoresponse force microscopy. The calculated vertical piezocoefficient is about 1.4 nm V(-1), that is, much higher than that of the conventional piezoelectric materials such as lead zirconate titanate and comparable to that of relaxor single crystals. The observed piezoresponse and achieved strain in graphene are associated with the chemical interaction of graphene's carbon atoms with the oxygen from underlying SiO2. The results provide a basis for future applications of graphene layers for sensing, actuating and energy harvesting.

  9. Molecular self-assembly on graphene on SiO2 and h-BN substrates.

    PubMed

    Järvinen, Päivi; Hämäläinen, Sampsa K; Banerjee, Kaustuv; Häkkinen, Pasi; Ijäs, Mari; Harju, Ari; Liljeroth, Peter

    2013-07-10

    One of the suggested ways of controlling the electronic properties of graphene is to establish a periodic potential modulation on it, which could be achieved by self-assembly of ordered molecular lattices. We have studied the self-assembly of cobalt phthalocyanines (CoPc) on chemical vapor deposition (CVD) grown graphene transferred onto silicon dioxide (SiO2) and hexagonal boron nitride (h-BN) substrates. Our scanning tunneling microscopy (STM) experiments show that, on both substrates, CoPc forms a square lattice. However, on SiO2, the domain size is limited by the corrugation of graphene, whereas on h-BN, single domain extends over entire terraces of the underlying h-BN. Additionally, scanning tunneling spectroscopy (STS) measurements suggest that CoPc molecules are doped by the substrate and that the level of doping varies from molecule to molecule. This variation is larger on graphene on SiO2 than on h-BN. These results suggest that graphene on h-BN is an ideal substrate for the study of molecular self-assembly toward controlling the electronic properties of graphene by engineered potential landscapes.

  10. Dielectric Properties of Porous Si3N4-SiO2-BN Composites

    NASA Astrophysics Data System (ADS)

    Sun, Yinbao; Zhang, Yumin; Li, Dihong; Han, Jiecai

    Porous Si3N4-SiO2-BN composites were prepared by adding starch as both pore former and consolidator. Bruggeman effective-medium model, Maxwell-Garnett model and logarithmic model were used to describe and predict the dielectric constant of porous Si3N4-SiO2-BN ceramics. Relative dielectric constant of porous Si3N4-SiO2-BN composites decreases with the increase of apparent porosity within limits, and these models can forecast the change of the dielectric constant of the porous ceramics quite well. The minimum relative dielectric constant is 2.5 at the apparent porosity of 0.555 at room-temperature. The relationship between dielectric constant and temperature were investigated. It was found dielectric constant varied a lot with the increase of temperature, and Debye relaxation theory was employed to explain the variation of the dielectric constant with temperature increment. But the Debye relaxation theory can not explain the reason of variation of dielectric constant at the temperature range from 300°C to 900°C. To ascertain the cause of changes of dielectric constant at this temperature region, differential scanning calorimentry (DSC) measurement was performed. In this temperature region, phase transition behavior occurs at nearly 300°C in the porous composites. The new phase probably has a tidy large dielectric constant, and the dielectric constant increases sharply.

  11. SiO2 nanoparticles change colour preference and cause Parkinson's-like behaviour in zebrafish.

    PubMed

    Li, Xiang; Liu, Bo; Li, Xin-Le; Li, Yi-Xiang; Sun, Ming-Zhu; Chen, Dong-Yan; Zhao, Xin; Feng, Xi-Zeng

    2014-01-22

    With advances in the development of various disciplines, there is a need to decipher bio-behavioural mechanisms via interdisciplinary means. Here, we present an interdisciplinary study of the role of silica nanoparticles (SiO2-NPs) in disturbing the neural behaviours of zebrafish and a possible physiological mechanism for this phenomenon. We used adult zebrafish as an animal model to evaluate the roles of size (15-nm and 50-nm) and concentration (300 μg/mL and 1000 μg/mL) in SiO2-NP neurotoxicity via behavioural and physiological analyses. With the aid of video tracking and data mining, we detected changes in behavioural phenotypes. We found that compared with 50-nm nanosilica, 15-nm SiO2-NPs produced greater significant changes in advanced cognitive neurobehavioural patterns (colour preference) and caused potentially Parkinson's disease-like behaviour. Analyses at the tissue, cell and molecular levels corroborated the behavioural results, demonstrating that nanosilica acted on the retina and dopaminergic (DA) neurons to change colour preference and to cause potentially Parkinson's disease-like behaviour.

  12. SiO2 nanoparticles change colour preference and cause Parkinson's-like behaviour in zebrafish

    PubMed Central

    Li, Xiang; Liu, Bo; Li, Xin-Le; Li, Yi-Xiang; Sun, Ming-Zhu; Chen, Dong-Yan; Zhao, Xin; Feng, Xi-Zeng

    2014-01-01

    With advances in the development of various disciplines, there is a need to decipher bio-behavioural mechanisms via interdisciplinary means. Here, we present an interdisciplinary study of the role of silica nanoparticles (SiO2-NPs) in disturbing the neural behaviours of zebrafish and a possible physiological mechanism for this phenomenon. We used adult zebrafish as an animal model to evaluate the roles of size (15-nm and 50-nm) and concentration (300 μg/mL and 1000 μg/mL) in SiO2-NP neurotoxicity via behavioural and physiological analyses. With the aid of video tracking and data mining, we detected changes in behavioural phenotypes. We found that compared with 50-nm nanosilica, 15-nm SiO2-NPs produced greater significant changes in advanced cognitive neurobehavioural patterns (colour preference) and caused potentially Parkinson's disease-like behaviour. Analyses at the tissue, cell and molecular levels corroborated the behavioural results, demonstrating that nanosilica acted on the retina and dopaminergic (DA) neurons to change colour preference and to cause potentially Parkinson's disease-like behaviour. PMID:24448416

  13. Programmed Synthesis by Stimuli-Responsive DNAzyme-Modified Mesoporous SiO2 Nanoparticles.

    PubMed

    Balogh, Dora; Aleman Garcia, Miguel Angel; Albada, H Bauke; Willner, Itamar

    2015-09-28

    DNAzyme-capped mesoporous SiO2 nanoparticles (MP SiO2 NPs) are applied as stimuli-responsive containers for programmed synthesis. Three types of MP SiO2 NPs are prepared by loading the NPs with Cy3-DBCO (DBCO=dibenzocyclooctyl), Cy5-N3 , and Cy7-N3 , and capping the NP containers with the Mg(2+) , Zn(2+) , and histidine-dependent DNAzyme sequences, respectively. In the presence of Mg(2+) and Zn(2+) ions as triggers, the respective DNAzyme-capped NPs are unlocked, leading to the "click" reaction product Cy3-Cy5. In turn, in the presence of Mg(2+) ions and histidine as triggers the second set of DNAzyme-capped NPs is unlocked leading to the Cy3-Cy7 conjugated product. The unloading of the respective NPs and the time-dependent formation of the products are followed by fluorescence spectroscopy (FRET). A detailed kinetic model for the formation of the different products is formulated and it correlates nicely with the experimental results.

  14. Dispersion of SiO2-based nanocomposites with high performance liquid chromatography.

    PubMed

    Wang, Jun; White, William B; Adair, James H

    2006-03-16

    Core-shell structured Ag/SiO2 nanocomposite has been synthesized by a cyclohexane/Igepal/water reverse micelle system. The spherical nanocomposite particles were washed and concentrated with high performance liquid chromatography (HPLC) to remove the surfactant added during synthesis. Spherical SiO2 micrometer-scale particles were packed in the HPLC column as a stationary phase for the washing and dispersing of Ag/SiO2 nanocomposite particles. Surface modification of Ag/SiO2 nanocomposite particles and SiO2 microspheres with silane coupling agent enhanced the surface charge of the particles and improved the efficiency of washing with HPLC. Well-dispersed Ag/SiO2 stable suspensions were successfully attained in ethanol/water mixed solvents after HPLC washing. The state of dispersion for the Ag/SiO2 nanocomposite suspension was systematically assessed using dynamic light scattering (DLS) and transmission electron microscope (TEM) and spin coat/atomic force microscope (AFM) analyses. The mechanism of the enabling HPLC washing protocol for SiO2-based nanoparticles is discussed.

  15. SiO2 aerosol nanoparticle reactor for occupational health and safety studies.

    PubMed

    Ostraat, Michele L; Swain, Keith A; Krajewski, James J

    2008-06-01

    Important questions are emerging about potential occupational safety, toxicological, and ecotoxicological effects and occupational inhalation exposure risks to engineered aerosol nanoparticles. Although multiple avenues are available to synthesize nanoparticles, few tools are accessible to industrial hygienists and inhalation toxicologists to produce well-characterized aerosols of known aerosol size distribution and particle number concentration that are stable, simple, and robust to operate. This article describes a SiO(2) aerosol nanoparticle reactor that has been developed as a tool for the study of the safety, health, and environmental consequences of exposure to nanoparticle synthesis and processing. The SiO(2) aerosol nanoparticle reactor is capable of stable, long-term synthesis of amorphous SiO(2) aerosol nanoparticles from d(50) = 10-70 nm at particle concentrations approximately 10(4)-10(7)particles/cm(3) that does not produce halogen-containing byproducts and does not require daily monitoring of the particle size distribution. This reactor is designed to produce a well-characterized aerosol to enable subsequent testing with a continuous, stable supply of aerosol nanoparticles (i) to facilitate inhalation toxicology studies, (ii) to measure explosion characteristics of aerosol nanoparticles, (iii) to determine the barrier efficacy for respirator filtration, bag house exhaust, and personal protective garment media challenged with diverse aerosol nanoparticles, and (iv) to develop airborne monitoring technologies for verifying workplace safety protocols. This article details reactor design, synthesis parameters, and instruments available to characterize the resulting aerosol nanoparticle size distributions.

  16. ZrO2-functionalized magnetic mesoporous SiO2 as effective phosphate adsorbent.

    PubMed

    Wang, Wenjuan; Zhou, Juan; Wei, Dan; Wan, Haiqin; Zheng, Shourong; Xu, Zhaoyi; Zhu, Dongqiang

    2013-10-01

    Phosphate pollution may cause eutrophication of the aquatic environment. In the present study, magnetic mesoporous SiO2 (denoted as MMS) and ZrO2-functionalized magnetic mesoporous SiO2 (denoted as ZrO2-MMS) were prepared and phosphate adsorption over the materials was investigated. The adsorbents were characterized by X-ray diffraction, transition electron microscopy, vibration sample magnetometer, N2 adsorption/desorption, zeta-potential measurement, and X-ray photoelectron spectroscopy. The results showed that MMS consisted of magnetite with particle sizes of 10-20 nm and ordered mesoporous SiO2 with the most probable pore diameter of 2.0 nm. The adsorbents could be readily separated and recovered under external magnetic field. The surface grafting of ZrO2 onto MMS led to an increase in surface zeta potential due to the formation of covalently linked ZrO2 functionality on the surface of MMS. Moreover, ZrO2 functionalization resulted in enhanced phosphate adsorption. Phosphate adsorption isotherms over the adsorbents could be well described by the Freundlich model. Phosphate adsorption kinetics followed the pseudo-second-order kinetics and the adsorption rate decreased with initial phosphate concentration. Additionally, increasing pH led to suppressed phosphate adsorption, and phosphate adsorption slightly increased with ionic strength.

  17. Mechanical properties testing of kapok fiber and its SiO2 composite

    NASA Astrophysics Data System (ADS)

    Xia, Re; Li, Xide

    2008-11-01

    Natural fiber polymer composites have various potential applications because of its particular property. In this paper, the template technique is employed to prepare SiO2/kapok fiber composite and the mechanical properties of the kapok fibril and its composite are presented. The mechanical tests are carried out on a probe platform which consists of a micro probe with a sharp tip, a micro-force sensor, and a micromanipulator and operates under an optical microscope. The probe platform has a high accurate load and displacement resolutions that are able to meet the requirements of the measurements. During the tests, the probe is controlled by the manipulator to exert lateral force at the midpoint of the kapok fibers which is clamed as a tension spring on a frame. The force is detected by the force sensor and consecutive deformation images of kapok and SiO2/kapok fibers are acquired by the optical microscopic systems. From consistently fitting the measured deformation profiles follows the more accurate calculation model. Thus, the mechanical properties, such as the load-displacement (stress-strain) curve, the elastic modulus of the kapok and SiO2/kapok fibers under different gripping conditions are obtained.

  18. Tribological evaluation of an Al2O3-SiO2 ceramic fiber candidate for high temperature sliding seals

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Steinetz, Bruce

    1994-01-01

    A test program to determine the relative sliding durability of an alumina-silica candidate ceramic fiber for high temperature sliding seal applications is described. Pin-on-disk tests were used to evaluate the potential seal material by sliding a tow or bundle of the candidate ceramic fiber against a superalloy test disk. Friction was measured during the tests and fiber wear, indicated by the extent of fibers broken in the tow or bundle, was measured at the end of each test. Test variables studied included ambient temperatures from 25 to 900 C, loads from 1.3 to 21.2 N, and sliding velocities from 0.025 to 0.25 m/sec. In addition, the effects of fiber diameter and elastic modulus on friction and wear were measured. Thin gold films deposited on the superalloy disk surface were evaluated in an effort to reduce friction and wear of the fibers. In most cases, wear increased with test temperature. Friction ranged from 0.36 at 500 C and low velocity (0.025 m/sec) to over 1.1 at 900 C and high velocity (0.25 m/sec). The gold films resulted in satisfactory lubrication of the fibers at 25 C. At elevated temperatures diffusion of substrate elements degraded the films. These results indicate that the alumina-silica (Al2O3-SiO2) fiber is a good candidate material system for high temperature sliding seal applications. More work is needed to reduce friction.

  19. Self-cleaning cotton functionalized with TiO2/SiO2: focus on the role of silica.

    PubMed

    Pakdel, Esfandiar; Daoud, Walid A

    2013-07-01

    This manuscript aims to investigate the functionalization of cotton fabrics with TiO2/SiO2. In this study, the sol-gel method was employed to prepare titania and silica sols and the functionalization was carried out using the dip-pad-dry-cure process. Titanium tetra isopropoxide (TTIP) and tetra ethyl orthosilicate (TEOS) were utilized as precursors of TiO2 and SiO2, respectively. TiO2/SiO2 composite sols were prepared in three different Ti:Si molar ratios of 1:0.43, 1:1, and 1:2.33. The self-cleaning property of cotton samples functionalized with TiO2/SiO2 was assessed based on the coffee stain removal capability and the decomposition rate of methylene blue under UV irradiation. FTIR study of the TiO2/SiO2 photocatalyst confirmed the existence of Si-O-Si and Ti-O-Si bonds. Scanning electron microscopy was employed to investigate the morphology of the functionalized cotton samples. The samples coated with TiO2/SiO2 showed greater ability of coffee stain removal and methylene blue degradation compared with samples functionalized with TiO2 demonstrating improved self-cleaning properties. The role of SiO2 in improving these properties is also discussed.

  20. Application of empirical ionic models to SiO 2 liquid: Potential model approximations and integration of SiO 2 polymorph data

    NASA Astrophysics Data System (ADS)

    Erikson, Robert L.; Hostetler, Charles J.

    1987-05-01

    Structural and thermodynamic properties of crystalline SiO 2 and SiO 2 liquid have been examined with Monte Carlo (MC), molecular dynamics (MD), and energy minimization (EM) calculations using several ionic potential models obtained from the literature. The MC and MD methods calculate the same structural and thermodynamic properties for liquids when the same potential model is used. The Ewald (1921) method of calculating coulomb interactions reproduced most successfully the structure of liquid silica. Approximating the coulomb interaction by eliminating the inverse lattice sum results in predicted bond distances that are too short and an average angle of approximately 180°. Introduction of a cut-off in the potential energy function produces irregular tetrahedra and inconsistencies in predicted Si-O coordination in silica liquid. The system internal energies show that liquid structures derived from random starting configurations can be metastable relative to structures calculated from crystalline starting configurations. The static lattice properties of the polymorphs alpha-quartz, coesite, and stishovite were used to evaluate further the accuracy of different sets of repulsive parameters for the full Ewald ionic model. Most of the models studied reproduced poorly the measured structures and elastic constants of the polymorphs. The major weakness of the ionic model is the unreasonably large Si-O bond strength (120 × 10 -12 ergs/bond) when formal ionic charges are used. Fractional charge models with a small Si-O bond strength (30 × 10 -12 ergs/bond) improve the agreement with experimental data. However, further improvement of the ionic model should include reducing the Si-O bond strength to values in better agreement with published estimates (7 × 10 - 12 to 13 × 10 -12 ergs/bond). By using additional information to constrain the parameterization of the ionic model, such as estimated bond strengths and static properties of the silica polymorphs, a model more representative of the interparticle interactions may be obtained.

  1. Photocatalytic activity of the binary composite CeO2/SiO2 for degradation of dye

    NASA Astrophysics Data System (ADS)

    Phanichphant, Sukon; Nakaruk, Auppatham; Channei, Duangdao

    2016-11-01

    In this study, CeO2 photocatalyst was modified by composite with SiO2 to increase efficiency and improve photocatalytic activity. The as-prepared SiO2 particles have been incorporated into the precursor mixture of CeO2 by homogeneous precipitation and subsequent calcination process. The phase compositions of CeO2 before and after compositing with SiO2 were identified by X-ray diffraction (XRD). The morphology and particle size of CeO2/SiO2 composite was analyzed by high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). The results showed SiO2 spheres with the particle size approximately 100-120 nm, and a uniform layer of CeO2 nanoparticles with a diameter of about 5-7 nm that were fully composite to the surfaces of SiO2. The X-ray photoelectron spectroscopy (XPS) technique was carried out in order to characterize the change in valence state and composite characteristic by shifted peaks of binding energies. The photocatalytic activity was studied through the degradation of Rhodamine B in aqueous solution under visible light exposure. The highest photocatalytic efficiency of CeO2/SiO2 composite was also obtained. To explain the high photocatalytic efficiency of CeO2/SiO2 composite, the proposed mechanism involves the high surface properties of the CeO2/SiO2 composite, as measured by Brunauer-Emmett-Teller (BET) method.

  2. 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.

  3. Localized surface plasmons in structures with linear Au nanoantennas on a SiO2/Si surface

    PubMed Central

    Milekhin, Ilya A; Kuznetsov, Sergei A; Rodyakina, Ekaterina E; Latyshev, Alexander V; Zahn, Dietrich R T

    2016-01-01

    The study of infrared absorption by linear gold nanoantennas fabricated on a Si surface with underlying SiO2 layers of various thicknesses allowed the penetration depth of localized surface plasmons into SiO2 to be determined. The value of the penetration depth derived experimentally (20 ± 10 nm) corresponds to that obtained from electromagnetic simulations (12.9–30.0 nm). Coupling between plasmonic excitations of gold nanoantennas and optical phonons in SiO2 leads to the appearance of new plasmon–phonon modes observed in the infrared transmission spectra the frequencies of which are well predicted by the simulations. PMID:28144502

  4. Preparation of monodisperse SiO2 nanoparticles by membrane emulsification using ideally ordered anodic porous alumina.

    PubMed

    Yanagishita, Takashi; Tomabechi, Yasuyuki; Nishio, Kazuyuki; Masuda, Hideki

    2004-02-03

    Monodisperse SiO2 particles of nanometer dimensions were fabricated by membrane emulsification using ideally ordered anodic porous alumina. For the preparation of monodisperse emulsion droplets, the dispersed phase was pressed through a porous alumina membrane into the continuous phase. After solidification treatment of the emulsion droplets, prepared spherical SiO2 nanoparticles with uniform sizes were obtained. From scanning electron microscope observation of the obtained particles, it was confirmed that the size distribution of SiO2 nanoparticles is relatively narrow.

  5. Photophysical properties of organic fluorescent probes on nanosized TIO 2/SIO 2 systems prepared by the sol-gel method

    NASA Astrophysics Data System (ADS)

    Eremenko, A.; Smirnova, N.; Rusina, O.; Linnik, O.; Eremenko, T. B.; Spanhel, L.; Rechthaler, K.

    2000-10-01

    Highly transparent TiO 2 and TiO 2/SiO 2 films prepared using the sol-gel technique have been studied by means of fluorescence probes method. Electronic interactions between adsorbed species—pyrene and donor-acceptor substituted push-pull stilbene—and Ti-doped silica matrices have been studied by the methods of steady-state and momentary spectrofluorimetry. Organic molecules are strongly adsorbed on the TiO 2 and Ti/Si surfaces. Increasing the Ti content within Ti/Si systems results in a decrease in the intensity of the photoluminescence spectra. These findings indicate that titania oxide species are highly dispersed within silica matrices, probably without aggregating each other, and adsorbed molecules are in direct contact with titanium ions located on the Ti/Si surface. The time scale of these decay processes is tens of nanoseconds. The fluorescence emission quenching can be attributed to the charge injection from the singlet excited state of the molecule to the conduction band of the semiconductor.

  6. Electron escape depth variation in thin SiO2 films measured with variable photon energy

    NASA Technical Reports Server (NTRS)

    Hecht, M. H.; Grunthaner, F. J.; Pianetta, P.; Johansson, L. I.; Lindau, I.

    1984-01-01

    A double crystal monochromator at the Stanford Synchrotron Radiation Laboratory is used to study the Si/SiO2 interface, using photon energies of hv = 1950-3700 eV. This photon energy range allows interfaces to be observed through oxide layers 50 A thick or more. Variations in electron escape depth and/or oxide density as a function of distance from the interface are observed over the entire kinetic energy range (100-3600 eV). These differences are attributed to a strained oxide layer near the interface.

  7. A Nonvolatile MOSFET Memory Device Based on Mobile Protons in SiO(2) Thin Films

    SciTech Connect

    Vanheusden, K.; Warren, W.L.; Devine, R.A.B.; Fleetwood, D.M.; Draper, B.L.; Schwank, J.R.

    1999-03-02

    It is shown how mobile H{sup +} ions can be generated thermally inside the oxide layer of Si/SiO{sub 2}/Si structures. The technique involves only standard silicon processing steps: the nonvolatile field effect transistor (NVFET) is based on a standard MOSFET with thermally grown SiO{sub 2} capped with a poly-silicon layer. The capped thermal oxide receives an anneal at {approximately}1100 C that enables the incorporation of the mobile protons into the gate oxide. The introduction of the protons is achieved by a subsequent 500-800 C anneal in a hydrogen-containing ambient, such as forming gas (N{sub 2}:H{sub 2} 95:5). The mobile protons are stable and entrapped inside the oxide layer, and unlike alkali ions, their space-charge distribution can be controlled and rapidly rearranged at room temperature by an applied electric field. Using this principle, a standard MOS transistor can be converted into a nonvolatile memory transistor that can be switched between normally on and normally off. Switching speed, retention, endurance, and radiation tolerance data are presented showing that this non-volatile memory technology can be competitive with existing Si-based non-volatile memory technologies such as the floating gate technologies (e.g. Flash memory).

  8. Pre-Oxidation Anneal Kinetics: Interface Degradation of Thin SIO2 Films on Silicon

    DTIC Science & Technology

    1992-07-13

    set describing the dependance of Io on the PreOxA time is shown in Fig. 3. From the fit of the data (solid line), and considering scatter in the data...300 360 420 480 540600 0 6 12 13 24 30 36 42 48 54 60 tA (8C) HzO conc. (ppmV) Figure 3. Typical dependance of I0 on PreOxA Figure 4. Dependance of

  9. Direct growth of patterned graphene on SiO2 substrates without the use of catalysts or lithography.

    PubMed

    Kim, Yong Seung; Joo, Kisu; Jerng, Sahng-Kyoon; Lee, Jae Hong; Yoon, Euijoon; Chun, Seung-Hyun

    2014-09-07

    We demonstrate a one-step fabrication of patterned graphene on SiO2 substrates through a process free from catalysts, transfer, and lithography. By simply placing a shadow mask during the plasma enhanced chemical vapor deposition (PECVD) of graphene, an arbitrary shape of graphene can be obtained on SiO2 substrate. The formation of graphene underneath the shadow mask was effectively prevented by the low-temperature, catalyst-free process. Growth conditions were optimized to form polycrystalline graphene on SiO2 substrates and the crystalline structure was characterized by Raman spectroscopy and transmission electron microscopy (TEM). Patterned graphene on SiO2 functions as a field-effect device by itself. Our method is compatible with present device processing techniques, and should be highly desirable for the proliferation of graphene applications.

  10. [Synthesis of SiO2 coated Eu(TTA)3phen and study on its fluorescent property].

    PubMed

    Tao, Dong-liang; Cui, Yu-min; Qiao, Rui; Xu, Yi-zhuang; Wu, Jin-guan

    2011-03-01

    New-style fluorescent material of SiO2/Eu(TTA)3 phen was synthesized by the method of dispersing Eu(TTA)3 phen in isopropanol and hydrolyzing TEOS. Fluorescence spectra showed that the emission intensities of SiO2/Eu(TTA)3 phen were much more stronger than that of Eu(TTA)3 phen by more than two times. At the same time, the peak at 617.4 nm became very sharp, which could not be observed for Eu(TTA)3 phen. This indicated that the structure of Eu(TTA)3 phen became more rigid after coated by SiO2. Thus, the emission intensity was enhanced largely. Life-time of SiOz/Eu(TTA)3 phen decreasing just confirmed the rigidity of SiO2/Eu(TTA)3 phen.

  11. Broadband NIR emission in novel sol-gel Er3+-doped SiO2-Nb2O5 glass ceramic planar waveguides for photonic applications

    NASA Astrophysics Data System (ADS)

    Aquino, Felipe Thomaz; Ferrari, Jefferson Luis; Ribeiro, Sidney José Lima; Ferrier, Alban; Goldner, Philippe; Gonçalves, Rogéria Rocha

    2013-01-01

    This paper reports on the sol-gel preparation and structural and optical characterization of new Er3+-doped SiO2-Nb2O5 nanocomposite planar waveguides. Erbium-doped (100-x)SiO2-xNb2O5 waveguides were deposited on silica-on-silicon substrates and Si(1 0 0) by the dip-coating technique. The waveguides exhibited uniform refractive index distribution across the thickness, efficient light injection at 1538 nm, and low losses at 632 and 1538 nm. The band-gap values lied between 4.12 eV and 3.55 eV for W1-W5, respectively, showing an excellent transparency in the visible and near infrared region for the waveguides. Fourier Transform Infrared (FTIR) Spectroscopy analysis evidenced SiO2-Nb2O5 nanocomposite formation with controlled phase separation in the films. The HRTEM and XRD analyses revealed Nb2O5 orthorhombic T-phase nanocrystals dispersed in a silica-based host. Photoluminescence (PL) analysis showed a broad band emission at 1531 nm, assigned to the 4I13/2 → 4I15/2 transition of the Er3+ ions present in the nanocomposite, with a full-width at half medium of 48-68 nm, depending on the niobium content and annealing. Hence, these waveguides are excellent candidates for application in integrated optics, especially in EDWA and WDM devices.

  12. Thermal conductivity and electrical properties of hybrid SiO2-graphene naphthenic mineral oil nanofluid as potential transformer oil

    NASA Astrophysics Data System (ADS)

    Qing, Soo Hui; Rashmi, W.; Khalid, M.; Gupta, T. C. S. M.; Nabipoor, M.; Taghi Hajibeigy, Mohammad

    2017-01-01

    Hybrid SiO2-graphene nanoparticles were synthesised by sol gel centrifugation technique under four different pH levels ranging from 9 to 12. Stability, thermal conductivity, viscosity and electrical conductivity of hybrid SiO2-graphene and pure graphene dispersed in naphthenic oil were investigated. Nanofluids were synthesied at three different nanoparticle concentrations (0.01, 0.04 and 0.08 wt%) while the temperature was varied from 20 °C to 100 °C. Field emission scanning electron microscopy (FESEM), x-ray spectroscopy and Fourier transform infrared (FTIR) spectrometer show successful coating of SiO2 on graphene surface. The growth units and size distribution of SiO2 nanoparticles increased with pH level. Moreover, the presence of SiO2 improved the dispersion behaviour of the nanofluid as confirmed by visual observation and UV–Vis studies. Zeta potential measurements show the hybrid nanofluids at pH 11 are most stable due to its optimum amount and size of SiO2 coated on graphene surface while at pH 12 shows least stability due to precipitation. The presence of SiO2 on graphene further enhanced the thermal conductivity by 80% at pH 9. Also, the viscosity of hybrid nanofluids was higher than pure graphene based nanofluids due to increase in density and particle size. Moreover, the addition of hybrid SiO2-graphene nanoparticles significantly reduced the electrical conductivity enhancement of base fluid from 557% to 97%.

  13. Fabrication of graphene oxide decorated with Fe3O4@SiO2 for immobilization of cellulase

    NASA Astrophysics Data System (ADS)

    Li, Yue; Wang, Xiang-Yu; Jiang, Xiao-Ping; Ye, Jing-Jing; Zhang, Ye-Wang; Zhang, Xiao-Yun

    2015-01-01

    Fe3O4@SiO2-graphene oxide (GO) composites were successfully fabricated by chemical binding of functional Fe3O4@SiO2 and GO and applied to immobilization of cellulase via covalent attachment. The prepared composites were further characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. Fe3O4 nanoparticles (NPs) were monodisperse spheres with a mean diameter of 17 ± 0.2 nm. The thickness of SiO2 layer was calculated as being 6.5 ± 0.2 nm. The size of Fe3O4@SiO2 NPs was 24 ± 0.3 nm, similar to that of Fe3O4@SiO2-NH2. Fe3O4@SiO2-GO composites were synthesized by linking of Fe3O4@SiO2-NH2 NPs to GO with the catalysis of EDC and NHS. The prepared composites were used for immobilization of cellulase. A high immobilization yield and efficiency of above 90 % were obtained after the optimization. The half-life of immobilized cellulase (722 min) was 3.34-fold higher than that of free enzyme (216 min) at 50 °C. Compared with the free cellulase, the optimal temperature of the immobilized enzyme was not changed; but the optimal pH was shifted from 5.0 to 4.0, and the thermal stability was enhanced. The immobilized cellulase could be easily separated and reused under magnetic field. These results strongly indicate that the cellulase immobilized onto the Fe3O4@SiO2-GO composite has potential applications in the production of bioethanol.

  14. [The study on DRS and Raman spectroscopy of surface modified TiO2/SiO2].

    PubMed

    Sang, Li-Xia; Zhong, Shun-He; Ma, Chong-Fang

    2007-04-01

    TiO2 /SiO2 were prepared by surface reaction of silica with an acetone solution of Ti(i-OC3H7)nCl(4-n), where n = 0-2. Results of XRD, Raman and UV-Vis DRS showed that two types of Ti species, small particles of anatase-type TiO2 and non-crystalline TiO(x) species, are molecularly dispersed on the silica surface. Relative to the TiO2 bulk, a blue-shift in the bandgap adsorption edge of TiO2/SiO2 was observed due to the quantum size effects. The bandgap energy (E(g)) of TiO2/SiO2 is 3.96 eV. When M(Pd, Cu, Ni) is deposited on TiO2/SiO2, the adsorption spectra extend to visible light region and the bandgap adsorption edge red shifts with respect to TiO2/SiO2. Compared with that of Pd, the deposition of Cu and Ni on TiO2/SiO2 has more effects on LMCT transition (O2- --> Ti4+) of Ti atoms. And the bandgap energy of Cu-TiO2 /SiO2 decreases to 3.69 eV. Similarly, the photon adsorption property for visible light can be improved relatively by the incorporation of MoO3 on TiO2/SiO2, At higher MoO3 loadings, the Mo-O-Ti coupled structure can be formed through the interaction between MoO3 and TiO2, which made the bandgap energy decrease to 3.81 eV.

  15. Selective adsorption of thiophenic compounds from fuel over TiO2/SiO2 under UV-irradiation.

    PubMed

    Miao, Guang; Ye, Feiyan; Wu, Luoming; Ren, Xiaoling; Xiao, Jing; Li, Zhong; Wang, Haihui

    2015-12-30

    This study investigates selective adsorption of thiophenic compounds from fuel over TiO2/SiO2 under UV-irradiation. The TiO2/SiO2 adsorbents were prepared and then characterized by N2 adsorption, X-ray diffraction and X-ray photoelectron spectroscopy. Adsorption isotherms, selectivity and kinetics of TiO2/SiO2 were measured in a UV built-in batch reactor. It was concluded that (a) with the employment of UV-irradiation, high organosulfur uptake of 5.12 mg/g was achieved on the optimized 0.3TiO2/0.7SiO2 adsorbent at low sulfur concentration of 15 ppmw-S, and its adsorption selectivity over naphthalene was up to 325.5; (b) highly dispersed TiO2 served as the photocatalytic sites for DBT oxidation, while SiO2 acted as the selective adsorption sites for the corresponding oxidized DBT using TiO2 as a promoter, the two types of active sites worked cooperatively to achieve the high adsorption selectivity of TiO2/SiO2; (c) The kinetic rate-determining step for the UV photocatalysis-assisted adsorptive desulfurization (PADS) over TiO2/SiO2 was DBT oxidation; (d) consecutive adsorption-regeneration cycles suggested that the 0.3TiO2/0.7SiO2 adsorbent can be regenerated by acetonitrile washing followed with oxidative air treatment. This work demonstrated an effective PADS approach to greatly enhance adsorption capacity and selectivity of thiophenic compounds at low concentrations for deep desulfurization under ambient conditions.

  16. Antireflection and SiO2 Surface Passivation by Liquid-Phase Chemistry for Efficient Black Silicon Solar Cells: Preprint

    SciTech Connect

    Yuan, H. C.; Oh, J.; Zhang, Y.; Kuznetsov, O. A.; Flood, D. J.; Branz, H. M.

    2012-06-01

    We report solar cells with both black Si antireflection and SiO2 surface passivation provided by inexpensive liquid-phase chemistry, rather than by conventional vacuum-based techniques. Preliminary cell efficiency has reached 16.4%. Nanoporous black Si antireflection on crystalline Si by aqueous etching promises low surface reflection for high photon utilization, together with lower manufacturing cost compared to vacuum-based antireflection coating. Ag-nanoparticle-assisted black Si etching and post-etching chemical treatment recently developed at NREL enables excellent control over the pore diameter and pore separation. Performance of black Si solar cells, including open-circuit voltage, short-circuit current density, and blue response, has benefited from these improvements. Prior to this study, our black Si solar cells were all passivated by thermal SiO2 produced in tube furnaces. Although this passivation is effective, it is not yet ideal for ultra-low-cost manufacturing. In this study, we report, for the first time, the integration of black Si with a proprietary liquid-phase deposition (LPD) passivation from Natcore Technology. The Natcore LPD forms a layer of <10-nm SiO2 on top of the black Si surface in a relatively mild chemical bath at room temperature. We demonstrate black Si solar cells with LPD SiO2 with a spectrum-weighted average reflection lower than 5%, similar to the more costly thermally grown SiO2 approach. However, LPD SiO2 provides somewhat better surface-passivation quality according to the lifetime analysis by the photo-conductivity decay measurement. Moreover, black Si solar cells with LPD SiO2 passivation exhibit higher spectral response at short wavelength compared to those passivated by thermally grown SiO2. With further optimization, the combination of aqueous black Si etching and LPD could provide a pathway for low-cost, high-efficiency crystalline Si solar cells.

  17. Heat flux induced dryout and rewet in thin films

    NASA Technical Reports Server (NTRS)

    Stroes, Gustave; Fricker, Darren; Issacci, Farrokh; Catton, Ivan

    1990-01-01

    Heat flux induced dryout of thin liquid films on an inclined copper plate was studied. Rewet of the dried out area is also considered. The four fluids used to form the thin films exhibited very different dryout and rewet characteristics. The contact angle and hysteresis effects were found to be important, but they must be considered in context with other parameters. No single variable was found to independently determine the pattern of dryout and rewet.

  18. Effect of SiO2 layer intermediation on direct carbothermal synthesis of SiC nanopowders.

    PubMed

    Hwang, Yeon; Riu, Doh-Hyung; An, Ju-Hyun; Chun, Dongil; Kim, Youngseok

    2013-09-01

    Beta-SiC was synthesized by direct carbothermal reaction using silicon and SiO2-layer-coated carbon powders. It is usually difficult to control the rate of the direct carbothermal reaction of silicon because the reaction rapidly progresses. Therefore coarse powders are obtained although it has the advantage of low synthesis temperature. To evade the above difficulty we tried to insert SiO2 layers between carbon and silicon powders, and the effect of SiO2 layer intermediation on the SiC synthesis was examined. SiO2 was coated on carbon black powders by using a 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) solution. The mixture of silicon and SiO2-coated carbon powders was reacted at 1200-1500 degrees C for 1 h in an Ar gas atmosphere. The morphologies of SiO2-coated carbon and synthesized SiC powders were observed. Thermal and phase evolution during the synthesis of SiC powders were analyzed. We obtained beta-SiC powders with a particle size of around 100 nm at the synthesis temperature of more than 1400 degrees C, which is a considerably lower reaction temperature than that of a usual carbothermal reaction.

  19. Photoluminescence and energy transfer investigation from SiO2: Tb, Au inverse opals to rhodamine-B dyes

    NASA Astrophysics Data System (ADS)

    Yang, Jianzhi; Yang, Zhengwen; Wang, Yida; Qiu, Jianbei; Song, Zhiguo

    2016-10-01

    Energy transfer has attracted extensive attention due to its widespread applications in medical diagnostics, DNA analysis and lighting devices. There are few reports on the energy transfer from rare earth ions to dyes. In the present work, the SiO2:Tb inverse opals with and without Au nanoparticles were prepared, and the organic rhodamine-B (RhB) dyes were filled into the voids of SiO2:Tb inverse opals. Non-radiative and radiative energy transfer processes from the SiO2:Tb inverse opals to the RhB were observed. The influence of Au nanoparticles and photonic band gap on the energy transfer from SiO2:Tb inverse opals to the RhB was investigated. The Au nanoparticles enhanced energy transfer was observed due to the surface plasmon resonance effects of the Au nanoparticles. When the emission peaks from the SiO2:Tb inverse opal is overlapped with the photonic band gap, the emission suppression of the SiO2:Tb inverse opal as well the emission enhancement of the RhB dyes were obtained, which is attributed to improved energy transfer caused by the photonic band gap. The steady state rate equations were used to explain enhancement of energy transfer caused by the photonic band gap.

  20. Radiation stability of SiO2 micro- and nanopowders under electron and proton exposure

    NASA Astrophysics Data System (ADS)

    Li, Chundong; Mikhailov, M. M.; Neshchimenko, V. V.

    2014-01-01

    The effects of proton and electron (E = 100 keV, F = 5 × 1015 сm-2) exposure on the reflective spectra of SiO2 micro- and nanopowders in wavelength range from 250 to 2500 nm have been investigated. It has been established that the reflectance and radiation stability of nanopowders is less than that of micropowders. This effect is caused by the high concentration of radiation defects, which act as surface absorption centers (Es‧ centers) near the energies 5.47 and 4.45 eV, and peroxide silicon defects (tbnd Sisbnd Osbnd Osbnd Sitbnd) near the energy 3.84 eV.

  1. Ion-implantation effect on time-dependent breakdown in SiO2

    NASA Technical Reports Server (NTRS)

    Li, S. P.

    1975-01-01

    It was experimentally demonstrated that the field emission of positive ions from the metal SiO2 interface in MOS structures can be controlled by introducing a positive charge in a small ion-implantation dose to a shallow depth below the metal electrode. Considerable improvement of time-dependent breakdown was noted in structures implanted in this manner as opposed to nonimplanted ones. This experiment confirms the model proposed by Li and Maserjian (1975) for radiation effect on time-dependent breakdown.

  2. Aligned Si3N4@SiO2 coaxial nanocables derived from a polymeric precursor

    NASA Astrophysics Data System (ADS)

    Fu, Xiuli; Peng, Zhijian; Zhu, Na; Wang, Chengbiao; Fu, Zhiqiang; Qi, Longhao; Miao, Hezhuo

    2010-06-01

    Well-aligned coaxial nanocables, composed of a crystalline α-Si3N4 inner core and amorphous SiO2 outer shell, were prepared on silicon substrates by pyrolysis of a preceramic polymer (perhydropolysilazane) with iron as catalyst. The nanocables have high density, and the longest nanocable can be up to millimeters. Photoluminescence measurement reveals a strong ultraviolet emission band centered at 360 nm and a weaker visible-light emission at 625 nm. The growth mechanism of the nanocables is discussed in detail.

  3. Fabrication of nickel nanocontacts using nanostencils and electron beam assisted SiO2 deposition.

    PubMed

    Langford, R M; Wang, T X

    2006-08-01

    Nickel nanocontacts for studying ballistic magnetoresistance have been fabricated by sputtering through FIB prepared nanostencil masks and by using electron beam assisted deposition of SiO2 to reduce the size of FIB milled pores through silicon nitride membranes. These two methods are discussed in terms of the nanocontact sizes, fabrication, and yield. The smallest size of the nanocontacts prepared using the nanostencil method was 40 nm and by the filling method was 1-2 nm. The maximum magnetoresistance measured was 1% and no evidence of a large ballistic magnetoresistance was observed.

  4. Formation of ge nanocrystals in SiO2 by electron beam evaporation.

    PubMed

    Basa, P; Molnár, G; Dobos, L; Pécz, B; Tóth, L; Tóth, A L; Koós, A A; Dózsa, L; Nemcsics, A; Horváth, Z J

    2008-02-01

    Ge nanocrystals were formed by electron beam evaporation on SiO2 covered Si substrates. The size and distribution of the nanocrystals were studied by atomic force microscopy, scanning electron microscopy and cross-sectional transmission electron microscopy. Dependencies of the nanocrystal size, of the nanocrystal surface coverage, and sheet resistance obtained by van der Pauw method of the Ge layer have been found on the evaporation time. The suggested growth mechanism for the formation of nanocrystals is the Volmer-Weber type. The sheet resistance exhibited a power dependence on the nanocrystal size.

  5. Electrospun SiO2 "necklaces" on unglazed ceramic tiles: a planarizing strategy

    NASA Astrophysics Data System (ADS)

    Di Mauro, Alessandro; Fragalà, Maria Elena

    2015-05-01

    Silica based nanofibres have been deposited on unglazed ceramic tiles by combining electrospinning and sol-gel processes. Poly(vinyl pyrrolidone) (PVP) alcoholic solutions and commercial spin on glass (Accuglass) mixtures have been used to obtain composite fibrous non-woven mats totally converted, after thermal annealing at 600 °C, to SiO2 microsphere "necklaces". The possibility to get an uniform fibres coverage onto the tile surface confirms the validity of electrospinning (easily scalable to large surface samples) as coating strategy to cover the macroscopic defects typical of the polished unglazed tile surface and improve surface planarization.

  6. The Obtaining of Nano Oxide Systems SiO2-REE with Alkoxide Technology

    NASA Astrophysics Data System (ADS)

    Amelina, Anna; Grinberg, Evgenii

    A lot of oxides systems with REE as dopants are used in catalytic processes in organic synthesis. They are very perspectives as thermostable coating in aerospace technics. These systems are usually based on silicon or aluminium oxides and doped with rare-earth elements. This systems can be produced by different methods. One of the most perspective of them is “sol-gel”-method with silicium, aluminium and rare-earth alkoxides as a precursor of doped silica and alumina, or their derivatives. Thus the obtaining of composite SiO _{2} - REE oxide materials by the hydrolysis doped with rare-earth elements was suggested. Some of alcoholate derivatives such as El(OR)n were used in this processes. The SiO _{2}- REE oxides were precipitated during the sol-gel process, where tetraethoxysilane (TEOS) as used as SiO _{2} sources. Also it is known that alkoxides of alkali metals, including lithium alkoxides, are widely used in industry and synthetic chemistry, as well as a source of lithium in various mixed oxide compositions, such as lithium niobate, lithium tantalate or lithium silicate. Therefore, we attempted to obtain the lithium silicate, which is also doped with rare-earth elements. Lithium silicate was obtained by alkaline hydrolysis of tetraethoxysilane with lithium alkoxide. Lithium alkoxide were synthesized by dissolving at metal in the corresponding alcohol are examined. The dependence of the rate of dissolving of the metal on the method of mixing of the reaction mixture and the degree of metal dispersion was investigated. The mathematical model of the process was composed and also optimization of process was carried out. Some oxide SiO _{2}, Al _{2}O _{3} and rare-earth nanostructured systems were obtained by sol-gel-method. The size of particle was determined by electron and X-ray spectroscopy and was in the range of 5 - 15 nm. Purity of this oxide examples for contaminating of heavy metals consists n.(1E-4...1E-5) wt%. Sols obtained by this method may be used for producing of thin coats on ceramics and metallic surfaces.

  7. Low-Power RIE of SiO2 in CHF3 To Obtain Steep Sidewalls

    NASA Technical Reports Server (NTRS)

    Turner, Tasha; Wu, Chi

    2003-01-01

    A reactive-ion etching (RIE) process has been developed to enable the formation of holes with steep sidewalls in a layer of silicon dioxide that covers a silicon substrate. The holes in question are through the thickness of the SiO2 and are used to define silicon substrate areas to be etched or to be built upon through epitaxial deposition of silicon. The sidewalls of these holes are required to be vertical in order to ensure that the sidewalls of the holes to be etched in the substrate or the sidewalls of the epitaxial deposits, respectively, also turn out to be vertical.

  8. High quality PECVD SiO2 process for recessed MOS-gate of AlGaN/GaN-on-Si metal-oxide-semiconductor heterostructure field-effect transistors

    NASA Astrophysics Data System (ADS)

    Lee, Jae-Gil; Kim, Hyun-Seop; Seo, Kwang-Seok; Cho, Chun-Hyung; Cha, Ho-Young

    2016-08-01

    A high quality SiO2 deposition process using a plasma enhanced chemical vapor deposition system has been developed for the gate insulator process of normally-off recessed-gate AlGaN/GaN metal-oxide-semiconductor-heterostructure field-effect transistors (MOS-HFETs). SiO2 films were deposited by using SiH4 and N2O mixtures as reactant gases. The breakdown field increased with increasing the N2O flow rate. The optimum SiH4/N2O ratio was 0.05, which resulted in a maximum breakdown field of 11 MV/cm for the SiO2 film deposited on recessed GaN surface. The deposition conditions were optimized as follows; a gas flow rate of SiH4/N2O (=27/540 sccm), a source RF power of 100 W, a pressure of 2 Torr, and a deposition temperature of 350 °C. A fabricated normally-off MOS-HFET exhibited a threshold voltage of 3.2 V, a specific on-resistance of 4.46 mΩ cm2, and a breakdown voltage of 810 V.

  9. Electroless nickel alloy deposition on SiO2 for application as a diffusion barrier and seed layer in 3D copper interconnect technology.

    PubMed

    Kim, Tae-Yoo; Son, Hwa-Jin; Lim, Seung-Kyu; Song, Young-Il; Park, Hwa-Sun; Suh, Su-Jeong

    2014-12-01

    Electroless Ni-P films were investigated with the aim of application as barrier and seed layers in 3D interconnect technology. Different shapes of blind-via holes were fabricated with a deep reactive ion etcher and SiO2 formed on these holes as an insulating layer. The surface of the substrate has been made hydrophilic by O2 plasma treatment with 100 W of power for 20 min. Electroless Ni-P films were deposited as both a diffusion barrier and a seed layer for Cu filling process. Prior to plating, substrates were activated in a palladium chloride solution after sensitization in a tin chloride solution with various conditions in order to deposit uniform films in TSV. After the formation of the electroless barrier layer, electro Cu was plated directly on the barrier layer. Ni-P films fabricated in blind-via holes were observed by scanning electron microscope. Energy dispersive spectroscopy line scanning was carried out for evaluating the diffusion barrier properties of the Ni-P films. The electroless Ni-P layer worked well as a Cu diffusion barrier until 300 degrees C. However, Cu ions diffused into barrier layer when the annealing temperature increases over 400 degrees C.

  10. Investigation of Leakage Current Mechanisms in La2O3/SiO2/4H-SiC MOS Capacitors with Varied SiO2 Thickness

    NASA Astrophysics Data System (ADS)

    Wang, Yucheng; Jia, Renxu; Zhao, Yanli; Li, Chengzhan; Zhang, Yuming

    2016-11-01

    In this study, the material and electrical properties of La2O3/SiO2/4H-SiC metal-oxide-semiconductor (MOS) capacitors are systematically characterized. Thermal oxidization SiO2 with varying thickness (0 nm, 3.36 nm, 5 nm, 8 nm, and 30 nm) were coated with La2O3 using atomic layer deposition on n-type 4H-SiC. The stacking oxides were measured using atomic force microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy, and the MOS capacitors were measured by capacitance-voltage and current-voltage measurements. The results demonstrate that the main gate current leakage mechanisms are dependent on the thickness of the SiO2 oxide under the applied electric field. The primary mechanism for current leakage from the La2O3/4H-SiC MOS capacitor follows the Schottky emission mechanism due to its low conduction band offset. In contrast, the current leakage mechanism for the capacitor with a 3.36 nm SiO2 layer follows the Poole-Frenkel emission mechanism on account of its high trap charge density in the gate dielectric and at the interface. When the thickness of the SiO2 layer increases to 8 nm, lower leakage current is observed by reason of the low trap charge density and high conduction band offset when E ≤ 5 MV/cm. As the electric field strength increases to 5 MV/cm and 5.88 MV/cm (30 nm SiO2: 4.8 MV/cm), the main current leakage mechanism changes to the Fowler-Nordheim tunneling mechanism, which indicates that the La2O3/SiO2 stacking structure can improve the properties of MOS capacitors.

  11. Formation Mechanism of SiO2-Type Inclusions in Si-Mn-Killed Steel Wires Containing Limited Aluminum Content

    NASA Astrophysics Data System (ADS)

    Wang, Kunpeng; Jiang, Min; Wang, Xinhua; Wang, Ying; Zhao, Haoqian; Cao, Zhanmin

    2015-10-01

    The origin, formation mechanism, and evolution of SiO2-type inclusions in Si-Mn-killed steel wires were studied by pilot trials with systematical samplings at the refining ladle, casting tundish, as-cast bloom, reheated bloom, and hot-rolled rods. It was found that the inclusions in tundish were well controlled in the low melting point region. By contrast, MnO-SiO2-Al2O3 inclusions in the as-cast bloom were with compositions located in the primary region of SiO2, and most CaO-SiO2-Al2O3-MnO inclusions lied in primary phase region of anorthite. Therefore, precipitation of SiO2 particles in MnO-SiO2-Al2O3 inclusions can be easier than in CaO-SiO2-Al2O3-MnO inclusions to form dual-phase inclusions in the as-cast bloom. Thermodynamic calculation by the software FactSage 6.4 (CRCT-ThermFact Inc., Montréal, Canada) showed that mass transfer between liquid steel and inclusions resulted in the rise of SiO2 content in inclusions from tundish to as-cast bloom and accelerated the precipitation of pure SiO2 phase in the formed MnO-SiO2-Al2O3 inclusions. As a result, the inclusions characterized by dual-phase structure of pure SiO2 in MnO-SiO2-Al2O3 matrix were observed in both as-cast and reheated blooms. Moreover, the ratio of such dual-phase SiO2-type inclusions witnessed an obvious increase from 0 to 25.4 pct before and after casting, whereas it changed little during the reheating and rolling. Therefore, it can be reasonably concluded that they were mainly formed during casting. Comparing the evolution of the inclusions composition and morphology in as-cast bloom and rolled products, a formation mechanism of the SiO2-type inclusions in wire rods was proposed, which included (1) precipitation of SiO2 in the formed MnO-SiO2-Al2O3 inclusion during casting and (2) solid-phase separation of the undeformed SiO2 precipitation from its softer MnO-SiO2-Al2O3 matrix during multipass rolling.

  12. Losses in TiO2/SiO2 multilayer coatings

    NASA Astrophysics Data System (ADS)

    Budasz, Jiří; Hutka, Jan; Václavík, Jan

    2016-11-01

    This paper deals with optical losses in the coatings consisting of a combination of titanium dioxide (TiO2) and silicon dioxide (SiO2) layers evaporated by the ion beam assisted deposition (IBAD). This combination is commonly used for optical coatings as a standard choice for antireflective or any other optical filter in the visible and near IR range. Although the technology has been known for decades, we point out that some undescribed parasite losses can still appear and we show how to deal with them. In fact, in some cases, the losses made the target coating even inapplicable. In this paper we try to investigate the origin of the losses and we describe the deposition parameters which allow us to reduce or completely remove them. We determined whether the losses are proportional to the total thickness of the coating or to the number of layers. The influence of scattering was measured as well. Deposition parameters which were studied are the substrate temperature, discharge voltage of the assisting ion gun, oxygen flow of the assisting ion gun and the deposition rate, especially its starting curve. Influence of the post process annealing was studied as well. Starting curve of the deposition rate of SiO2 layer and the amount of oxygen flowing through the assisting ion gun were found as a crucial parameters.

  13. Photon Irradiation Response on Ge and Al-Doped SiO2 Optical Fibres

    NASA Astrophysics Data System (ADS)

    Yaakob, Nor Haliza; Wagiran, Husin; Ramli, Ahmad Termizi; Ali, Hassan; Asni, Hazila

    2010-07-01

    Recently, research groups have reported a number of radiation effects on the applications of SiO2 optical fibres with possible use as dosimeter material because these optical fibre provide a good basis for medical radiation dosimetry. The objective of this study is to investigate the thermoluminescence response and fading characteristic for germanium and aluminium doped SiO2 optical fibres with photon irradiation. These optical fibres are placed in solid phantom and irradiated to 6 and 10 MV photon beam at dose ranging from 0.06 Gy to 0.24 Gy using Primus MLC 3339 linear accelerator at Hospital Sultan Ismail, Johor Bahru. In fading studies, the TL measurements were continued up to 14 days period. The optical fibres will produce glow curves whereby the information is then analyzed. Al and Ge-doped optical fibres have a linear dose-TL signal relationship that is proportionality between the TL signal and the doses. Comparison for TL response between different linear accelerator showed a good agreement because these optical fibres also have a linear dose-TL signal relationship even using different equipments.

  14. Study of the thermal treatment of SiO2 aggregate

    NASA Astrophysics Data System (ADS)

    Tahiri, N.; Khouchaf, L.; Elaatmani, M.; Louarn, G.; Zegzouti, A.; Daoud, M.

    2014-08-01

    Crystalline quality and the silanoles defects (Si-OH) present within the structure of natural SiO2 play an important role in its reactivity. In this work, the relationship between the loss of silanoles and the crystallinity improvement upon heating between 450 °C and 650 °C was shown using X-Ray Diffraction (XRD) and Fourier Transform mid Infrared Spectroscopy in Attenuated Total Reflection (ATR). A shift of the principal band Si-O-Si from 1078 cm-1 to 1082 cm-1 and the decrease of the intensity of the Si-OH bands at 555cm-1and at 950cm-1 upon heating between 450 °C and 650 °C were shown. The reduction of the band is correlated to the loss of silanoles. In agreement with FT-IR results, the decrease of the FWHM of the XRD peaks shows that the crystalline quality is improved upon heating. This result leads to a decrease of the reactivity of SiO2 aggregate under chemical attacks.

  15. Role of hydrogen in volatile behaviour of defects in SiO2-based electronic devices

    PubMed Central

    El-Sayed, Al-Moatasem; Gös, Wolfgang; Grasser, Tibor; Shluger, Alexander L.

    2016-01-01

    Charge capture and emission by point defects in gate oxides of metal–oxide–semiconductor field-effect transistors (MOSFETs) strongly affect reliability and performance of electronic devices. Recent advances in experimental techniques used for probing defect properties have led to new insights into their characteristics. In particular, these experimental data show a repeated dis- and reappearance (the so-called volatility) of the defect-related signals. We use multiscale modelling to explain the charge capture and emission as well as defect volatility in amorphous SiO2 gate dielectrics. We first briefly discuss the recent experimental results and use a multiphonon charge capture model to describe the charge-trapping behaviour of defects in silicon-based MOSFETs. We then link this model to ab initio calculations that investigate the three most promising defect candidates. Statistical distributions of defect characteristics obtained from ab initio calculations in amorphous SiO2 are compared with the experimentally measured statistical properties of charge traps. This allows us to suggest an atomistic mechanism to explain the experimentally observed volatile behaviour of defects. We conclude that the hydroxyl-E′ centre is a promising candidate to explain all the observed features, including defect volatility. PMID:27436969

  16. "Embedded Emitters": Direct bandgap Ge nanodots within SiO2

    NASA Astrophysics Data System (ADS)

    Kuo, M. H.; Chou, S. K.; Pan, Y. W.; Lin, S. D.; George, T.; Li, P. W.

    2016-12-01

    Microdisk-arrays of vertically stacked 30-70 nm Ge nanodots embedded within SiO2 were fabricated using thermal oxidation of Si0.75Ge0.25 abacus-shaped pillars and followed by post-annealing in oxygen-deficient conditions. The Ge nanodots are subjected to increasing quantum-confinement and tensile-strain by reducing dot size. We show that considerable quantum-confinement and tensile-strain can be generated within 30 nm Ge nanodots embedded in SiO2, as evidenced by large Raman red shifts for the Ge-Ge phonon lines in comparison to that for bulk Ge. These large quantum-confinement and tensile-strain facilitate direct-bandgap photoluminescence experimentally observed for the Ge nanodots, and are consistent with the strain-split photoluminescence transitions to the light-hole (LH) and heavy-hole (HH) valence bands at 0.83 eV and 0.88 eV, respectively. Time-resolved photoluminescence measurements conducted from 10-100 K show temperature-insensitive carrier lifetimes of 2.7 ns and 5 ns for the HH and LH valence-band transitions, respectively, providing additional strong evidence of direct bandgap photoluminescence for tensile-strained Ge nanodots.

  17. Atomistic Simulation of Environment-Assisted Crack Propagation Behavior of SiO2

    NASA Astrophysics Data System (ADS)

    Yasukawa, Akio

    A modified extended Tersoff interatomic potential function is proposed to simulate environment-assisted crack propagation behavior. First, the physical properties of Si, O2, H2, SiO2, and H2O were calculated by this modified function. It was confirmed that the calculated values agreed with the measured values very well. Next, the potential surface of the H2O molecular transporting process to the crack tip of SiO2 material was calculated by the same function. The relationship between the velocity of crack propagation "υ" and the stress intensity factor "K" was calculated based on this surface. The results agreed with the experimental results well. This simulation clarified that the crack velocity is controlled by the H2O transporting process in both regions I and II of the "υ-K curve". In region I, H2O molecules have physically limited access to the crack tip due to the small opening in the crack. This works as an energy barrier in transporting H2O molecules. Due to the relatively large crack opening in region II, H2O molecules have free access to the crack tip without any energy barrier. This difference makes a bend in the "υ-K curve" between regions I and II.

  18. Ultrahydrous stishovite from high-pressure hydrothermal treatment of SiO2

    PubMed Central

    Spektor, Kristina; Nylen, Johanna; Stoyanov, Emil; Navrotsky, Alexandra; Hervig, Richard L.; Leinenweber, Kurt; Holland, Gregory P.; Häussermann, Ulrich

    2011-01-01

    Stishovite (SiO2 with the rutile structure and octahedrally coordinated silicon) is an important high-pressure mineral. It has previously been considered to be essentially anhydrous. In this study, hydrothermal treatment of silica glass and coesite at 350–550 °C near 10 GPa produces stishovite with significant amounts of H2O in its structure. A combination of methodologies (X-ray diffraction, thermal analysis, oxide melt solution calorimetry, secondary ion mass spectrometry, infrared and nuclear magnetic resonance spectroscopy) indicate the presence of 1.3 ± 0.2 wt % H2O and NMR suggests that the primary mechanism for the H2O uptake is a direct hydrogarnet-like substitution of 4H+ for Si4+, with the protons clustered as hydroxyls around a silicon vacancy. This substitution is accompanied by a substantial volume decrease for the system (SiO2 + H2O), although the stishovite expands slightly, and it is only slightly unfavorable in energy. Stishovite could thus be a host for H2O at convergent plate boundaries, and in other relatively cool high-pressure environments. PMID:22160677

  19. Experimental study on the coalescence process of SiO2 supported colloidal Au nanoparticles

    NASA Astrophysics Data System (ADS)

    Ruffino, F.; Torrisi, V.; Grimaldi, M. G.

    2015-11-01

    We report on an experimental study of the coalescence-driven grow process of colloidal Au nanoparticles on SiO2 surface. Nanoparticles with 30, 50, 80, 100 nm nominal diameters on a SiO2 substrate were deposited, from solutions, by the drop-casting method. Then, annealing processes, in the 573-1173 K temperature range and 900-3600 s time range, were performed. Using scanning electron microscopy analyses, the temporal evolution of the nanoparticles sizes has been studied. In particular, for all classes of nanoparticles, the experimental-obtained diameters distributions evidenced double-peak shapes (i. e. bimodal distributions): a first peak centered (and unchanged changing the annealing temperature and/or time) at the nominal diameter of the as-deposited nanoparticles, , and a second peak shifting at higher mean diameters, , increasing the annealing temperature and/or time. This observation suggested us a coalescence-driven growth process of a nanoparticles sub-population. As a consequence, the temporal evolution of (for each class of nanoparticles and each annealing temperature), within the well-established particles coalescence theoretical framework, has been analyzed. In particular, by the analyses of the experimental data using relations as prescribed by the theoretical model, a characteristic size-dependent activation energy for the Au nanoparticles coalescence process has been evaluated.

  20. Surface chemical bonds, surface-enhanced Raman scattering, and dielectric constant of SiO2 nanospheres in-situ decorated with Ag-nanoparticles by electron-irradiation

    NASA Astrophysics Data System (ADS)

    Phatangare, A. B.; Dhole, S. D.; Dahiwale, S. S.; Mathe, V. L.; Bhoraskar, S. V.; Late, D. J.; Bhoraskar, V. N.

    2016-12-01

    Nanostructures of dielectric materials decorated with metal nanoparticles are of great scientific interest; however, the involved synthesis methods are complicated and require multistep chemical processing, including functionalization of the dielectric surfaces. In the present work, without chemical processes, silver nanoparticles of average sizes in the range of 11 to 15 nm were in-situ synthesized and decorated on SiO2 nanospheres in a single step process by irradiating a solution (AgNO3-polyvinylpyrrolidone (PVP)-SiO2 nanospheres) with 6 MeV electrons at 1.5 × 1015 e-/cm2, 3.0 × 1015 e-/cm2, and 4.5 × 1015 e-/cm2 fluences. The electron irradiated solutions were characterized with different surface and other techniques. The results revealed that the SiO2 nanospheres were uniformly decorated with Ag nanoparticles, and the prominent chemical bonds involved were Ag-O, Si-O-Ag, and Si-Ag. Moreover, the sizes and the decoration density of Ag nanoparticles could be tailored by varying electron fluence. The Surface-enhanced Raman scattering (SERS) of 4-aminothiophenol (4-ATP) solutions was studied using substrates in the form of thin coatings of the solutions of Ag-decorated SiO2 nanospheres. The appearance of the characteristic SERS peaks of both 4-ATP and 4, 4'-dimercaptoazobenzene (4, 4'-DMAB) in Raman spectra confirmed the conversion of a fraction of 4-ATP into 4, 4'-DMAB in the presence of Ag nanoparticles. Composites in the form of thin films were synthesized from the mixture solutions of PVP and Ag-decorated SiO2 nanospheres. The dielectric constant of each thin film was higher as compared to polymers, and could be tailored by varying electron fluence used for decorating Ag nanoparticles.

  1. Sign reversal of junction magnetoresistance in p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure: a possibility in spintronics application.

    PubMed

    Giri, S K; Nath, T K

    2012-10-01

    We have fabricated a p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure, consisting of a p-type manganite (La0.7Ca0.3MnO3) and n-type Si with a interfacial layer of SiO2 with typical thickness of about 9 nm using pulsed laser deposition technique. The junction exhibits rectifying behavior over the temperature range of 10-300 K with rectification factor 52 at room temperature. Investigation on the electrical properties of p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure exhibits nonlinear J-V characteristics in a wide temperature range. A crossover from negative to positive junction magnetoresistance (JMR) is observed in p-La0.7Ca0.3MnO3/SiO2/n-Si heterostructure in current perpendicular to film plane (CPP) geometry. The temperature dependent sign of junction magnetoresistance of the heterojunction has been investigated carefully in details. It is found that the junction exhibits the positive junction magnetoresistance when the temperature is greater than the ferromagnetic to paramagnetic transition temperature (Tc) of the top highly spin-polarized half-metallic ferromagnetic La0.7Ca0.3MnO3 manganite film layer. The relation between junction magnetoresistance and external magnetic field is found to be of (delta rho/rho approximately equal alphaHbeta) type having both alpha and beta temperature dependent. We attribute the emergence of negative JMR at lower temperature (< Tc) and positive JMR at higher temperature (> Tc) to the quantum mechanical tunneling transport mechanism across the heterojunction. Our results might be very useful to fabricate artificial devices using the manganite-based heterojunction grown on single crystalline n-Si (100) in spintronics device applications.

  2. The effects of surface polarity and dangling bonds on the electronic properties of MoS2 on SiO2

    NASA Astrophysics Data System (ADS)

    Sung, Ha-Jun; Choe, Duk-Hyun; Chang, Kee Joo

    2015-03-01

    MoS2 has recently attracted much attention due to its intriguing physical phenomena and possible applications for the next generation electronic devices. In pristine monolayer MoS2, strong spin-orbit coupling and inversion symmetry breaking allow for an effective coupling between the spin and valley degrees of freedom, inducing valley polarization at the K valleys. However, the spin-valley coupling disappears in bilayer MoS2 because the inversion symmetry is restored. In this work, we investigate the effects of surface polarity and dangling bonds on the electronic properties of MoS2 on α-quartz SiO2 through first-principles calculations. In monolayer MoS2, a transition can take place from the direct-gap to indirect-gap semiconductor in the presence of O dangling bonds. In bilayer MoS2, O dangling bonds induce dipole fields across the interface and thus break the inversion symmetry, resulting in the valley polarization, similar to that of pristine monolayer MoS2. Based on the results, we discuss the origin of the valley polarization observed in MoS2 deposited on SiO2 This work was supported by National Research Foundation of Korea (NRF) under Grant No. NRF-2005-0093845 and by Samsung Science and Technology Foundation under Grant No. SSTFBA1401-08.

  3. Optically- and thermally-stimulated luminescences of Ce-doped SiO2 glasses prepared by spark plasma sintering

    NASA Astrophysics Data System (ADS)

    Okada, Go; Kasap, Safa; Yanagida, Takayuki

    2016-11-01

    Rare-earth doped phosphors have been used in many applications including radiation measurements. In the latter applications, the radiation photons are converted to light so that we can indirectly detect the radiation using a conventional photodetector. In this work, we have prepared and characterized a Ce-doped SiO2 glass for dosimeter applications. Unlike conventional techniques such as sol-gel synthesis, the sample was prepared by spark plasma sintering. Although the PL emission seems to be only from the Ce3+ ions in the structure, due to the X-ray induced luminescence, we have also observed optically-stimulated luminescence (OSL), and thermally-stimulated luminescence (TSL), owing to a pair of silylenes and a set of dioxasilirane and silylene in addition to Ce3+. We have measured the detector response vs irradiation dose for both the OSL and TSL. The detector response in both cases is linear over the dose range from at least 1 mGy to 2 Gy. Particularly, the sensitivity of TSL is so high that it should be considered to be a good candidate for practical applications.

  4. Effect of SiO2 substrate on the irradiation-assisted manipulation of supported graphene: a molecular dynamics study.

    PubMed

    Zhao, Shijun; Xue, Jianming; Wang, Yugang; Yan, Sha

    2012-07-20

    The irradiation effects in graphene supported by SiO(2) substrate including defect production and implantation efficiency are investigated using the molecular dynamics (MD) method with empirical potentials. We show that the irradiation damage in supported graphene comes from two aspects: the direct damage induced by the incident ions and the indirect damage resulting from backscattered particles and sputtered atoms from the substrate. In contrast with the damage in suspended graphene, we find that the indirect damage is dominant in supported graphene at high energies. As a result, enhanced irradiation damage in supported graphene is observed when the incident energy is above 5 keV for Ar and 3 keV for Si. The direct damage probability at all energies, even the total damage probability at low energies, in supported graphene is always much lower than that in suspended graphene because of the higher threshold displacement energy of carbon atoms. In addition, we demonstrate the striking finding that it is possible to dope graphene with sputtered atoms from the substrate and the implantation probability is considerable at optimal energies. Our results indicate that the substrate is an important factor in the process of ion-irradiation-assisted engineering of the properties of graphene.

  5. SWNT nucleation from carbon-coated SiO2 nanoparticles via a vapor-solid-solid mechanism.

    PubMed

    Page, Alister J; Chandrakumar, K R S; Irle, Stephan; Morokuma, Keiji

    2011-01-26

    Since the discovery of single-walled carbon nanotubes (SWNTs) in the early 1990s, the most commonly accepted model of SWNT growth on traditional catalysts (i.e., transition metals including Fe, Co, Ni, etc.) is the vapor-liquid-solid (VLS) mechanism. In more recent years, the synthesis of SWNTs on nontraditional catalysts, such as SiO(2), has also been reported. The precise atomistic mechanism explaining SWNT growth on nontraditional catalysts, however, remains unknown. In this work, CH(4) chemical vapor deposition (CVD) and single-walled carbon nanotube (SWNT) nucleation on SiO(2) nanoparticles have been investigated using quantum-chemical molecular dynamics (QM/MD) methods. Upon supply of CH(x) species to the surface of a model SiO(2) nanoparticle, CO was produced as the main chemical product of the CH(4) CVD process, in agreement with a recent experimental investigation [Bachmatiuk et al., ACS Nano 2009, 3, 4098]. The production of CO occurred simultaneously with the carbothermal reduction of the SiO(2) nanoparticle. However, this reduction, and the formation of amorphous SiC, was restricted to the nanoparticle surface, with the core of the SiO(2) nanoparticle remaining oxygen-rich. In cases of high carbon concentration, SWNT nucleation then followed, and was driven by the formation of isolated sp(2)-carbon networks via the gradual coalescence of adjacent polyyne chains. These simulations indicate that the carbon saturation of the SiO(2) surface was a necessary prerequisite for SWNT nucleation. These simulations also indicate that a vapor-solid-solid mechanism, rather than a VLS mechanism, is responsible for SWNT nucleation on SiO(2). Fundamental differences between SWNT nucleation on nontraditional and traditional catalysts are therefore observed.

  6. Suppression of transverse-mode spurious responses for SAW resonators on SiO2/Al/LiNbO3 structure by selective removal of SiO2.

    PubMed

    Nakamura, Hiroyuki; Nakanishi, Hidekazu; Goto, Rei; Hashimoto, Ken-ya

    2011-10-01

    A SiO(2)/Al/LiNbO(3) structure has a large electromechanical coupling factor (K(2)) and good temperature coefficient of frequency (TCF) for applications as a SAW duplexer of the Universal Mobile Telecommunications System (UMTS) Band I. However, the SiO(2)/Al/LiNbO(3) structure also supports two unwanted spurious responses; one is caused by the Rayleigh mode and the other by the transverse mode. As the authors have previously discussed, the Rayleigh-mode spurious response can be suppressed by controlling the cross-sectional shape of a SiO(2) overlay deposited on resonator electrodes. In this paper, a new technique to suppress the transverse-mode spurious responses is proposed. In the technique, the SiO(2) overlay is selectively removed from the dummy electrode region. The spurious responses are analyzed by the laser probe system. The results indicate that the spurious responses in question were hybrid modes caused by the coupling between the main (SH) SAW and another (Rayleigh) SAW with different velocities. The hybrid-mode spurious behavior was dependent on the velocities in the IDT and the dummy regions (v(i) and v(d)). The hybrid-mode spurious responses could be suppressed by selectively removing SiO(2). Furthermore, the SAW energy confinement could be enhanced in the IDT electrode region when v(i) < v(d). The transverse-mode spurious responses were successfully suppressed without degrading the SAW resonator performances.

  7. Structural and optical properties of the In(x)Ga(1-x)As nanowires grown on SiO2 via vapor-liquid-solid method.

    PubMed

    Shin, Hyun Wook; Shin, Jae Cheol; Kim, Do Yang; Choi, Won Jun; Choe, Jeong-Woo

    2014-08-01

    We report the crystal growth of the In(x)Ga(1-x)As nanowires (NWs) on SiO2 substrate using metal organic chemical vapor deposition. Au nanoparticles which are disintegrated from thin Au film have been used as a catalyst for the vapor-liquid-solid growth. Electron microscopy characterization is performed to investigate the structural properties of the In(x)Ga(1-x)As NW. The In(x)Ga(1-x)As NW grown under an optimal condition has a single-crystal wurtzite structure without any misfit dislocation or stacking fault. Strong room temperature photoluminescence peaks are observed from In(x)Ga(1-x)As NWs passivated by GaAs. Very low light reflectance is measured at the NW surface in the wavelength range from 250 to 1200 nm. The single crystal In(x)Ga(1-x)As NWs are applicable to the various electrical and optical devices.

  8. Facile transfer of thickness controllable poly(methyl methacrylate) patterns on a nanometer scale onto SiO2 substrates via microcontact printing combined with simplified Langmuir-Schaefer technique.

    PubMed

    Kim, Yong-Kwan; Kim, Dae-Il; Park, Jaehyun; Shin, Gunchul; Kim, Gyu Tae; Ha, Jeong Sook

    2008-12-16

    We report on the facile patterning of poly(methyl methacrylate) (PMMA) layers onto SiO2 substrates via microcontact printing combined with the simplified Langmuir-Schaefer (LS) technique. Langmuir film of PMMA was formed just by dropping a dilute PMMA solution onto the air/water surface in a glass Petri dish via self-assembly, and it was used as an ink for the patterned poly(dimethylsilioxane) (PDMS) stamp. The transferred film properties were systematically investigated with variation of postannealing temperature, molecular weight of PMMA, and the inking number. The patterned PMMA film surface was smooth with no vacancy defect in a few micrometers scale AFM images over the whole film area after post-annealing process. The thickness of the PMMA patterns was controlled on the nanometer scale by the number of inkings of the LS layer of PMMA on the PDMS stamp. By using the PMMA patterns as a barrier and a sacrificial layer against the chemical etching and metal deposition, SiO2 and metal patterns were fabricated, respectively. The PMMA layers also worked as a passivation layer against the patterning of V2O5 nanowires and the selective adsorption of single-walled carbon nanotubes (SWCNTs). We also fabricated thin film transistors using patterned SWCNTs with different percolation states and investigated the electrical properties.

  9. VUV and Optical Emission Characterization of Fluorocarbon SiO2 Etch Processes and Correlation to Etch Feature Quality

    NASA Astrophysics Data System (ADS)

    Hsueh, H.; Dandapani, E.; McGrath, R.; Messier, R.; Ji, B.; Karwacki, E.

    2000-10-01

    Fluorocarbon discharges used for SiO2 etch were characterized using optical (OES) and VUV emission spectroscopy. Actinometry was used to monitor atomic fluorine concentration (N_F) as power, pressure and gas mix were varied. Thermal oxide films were photolithographically patterned to define 0.5-2.0 μ m trench features, and then etched in an AMAT Mark II reactor. Etch rate, selectivity and feature critical dimension were measured using SEM and other techniques. DC self-bias was also recorded for each set of process conditions. Good etch features, etch rates of 1175 Åmin, and selectivity of 7.9 were obtained for reactor operation at 750 W, 80 mTorr, and with a gas mixture of CF_4/CHF_3/Ar at 85/10/5 sccm. Etch rate, selectivity and feature critical dimensions observed have been correlated to actinometric estimates of N_F, to self-bias voltage and to OES and VUV emissions. While varying process conditions around the reference values defined above, NF was found to increase monotonically between 0.75 and 1.2x10^13/cm^3 as pressure was increased from 70 to 100 mTorr, as power was increased from 650 to 850 W, and as CF4 gas fraction was increased from 5the reference gas mixture, etch rate was found to increase (1150 to 1550 Åmin) with increasing power, and to decrease (1550 to 550 Åmin) with increasing pressure. In these cases, etch rate trend tracked the self-bias voltage established. However, when CF4 gas fraction was increased from 5Åmin, while NF concentration increased by only 15self-bias varied by only 8feature profiles, and associated reaction processes will be presented.

  10. Characterization of cinematographic films by Laser Induced Breakdown Spectroscopy

    NASA Astrophysics Data System (ADS)

    Gaspard, S.; Oujja, M.; Rebollar, E.; Abrusci, C.; Catalina, F.; Castillejo, M.

    2007-12-01

    The emulsion-coated transparent plastic-base film has been the main carrier for production and preservation of motion picture contents since the 19th century. The knowledge of the composition of black and white silver gelatine cinematographic films is of great importance for the characterization of the photographic process and for identifying the optimum conditions for conservation. A cinematographic film is a multi-component system that consists of a layer of photographic emulsion overcoating a polymeric support (plasticized cellulose triacetate) and a protective transparent cross-linked gelatine layer coating the emulsion. In the present work, Laser Induced Breakdown Spectroscopy (LIBS) is used to characterize the composition of the materials of cinematographic films. LIB spectra of film samples and of different individual film components, polymeric support and reference gelatines, were acquired in vacuum by excitation at 266 nm (Q-switched Nd:YAG laser, 6 ns, 10 Hz). In the cinematographic film, silver lines from the light-sensitive silver halide salts of the photographic emulsion are accompanied by iron, lead, chrome and phosphorus lines. Iron and lead are constituents of film developers, chrome is included in the composition of the hardening agents and phosphorus has its origin in the plasticizer used in the polymeric support. By applying successive pulses on the same spot of the film sample, it was possible to observe through stratigraphic analysis the different layers composition. Additionally, the results obtained reveal the analytical capacity of LIBS for the study and classification of the different gelatine types and qualities used for the protecting layer and the photographic emulsion.

  11. Structural and electrical characterization of NbO2 vertical devices grown on TiN coated SiO2/Si substrate

    NASA Astrophysics Data System (ADS)

    Joshi, Toyanath; Borisov, Pavel; Lederman, David

    Due to its relatively high MIT temperature (1081 K) and current-controlled negative differential resistance, NbO2 is a robust candidate for memory devices and electrical switching applications. In this work, we present in-depth analysis of NbO2 thin film vertical devices grown on TiN coated SiO2/Si substrates using pulsed laser deposition (PLD). Two of the films grown in 1 mTorr and 10 mTorr O2/Ar (~7% O2) mixed growth pressures were studied. The formation of NbO2 phase was confirmed by Grazing Incidence X-ray Diffractometry (GIXRD), X-ray Photoelectron Spectroscopy (XPS) and current vs. voltage measurements. A probe station tip (tip size ~2 μm) or conductive AFM tip was used as a top and TiN bottom layer was used as a bottom contact. Device conductivity showed film thickness and contact size dependence. Current pulse measurements, performed in response to applied triangular voltage pulses, showed a non-linear threshold switching behavior for voltage pulse durations of ~100 ns and above. Self-sustained current oscillations were analyzed in terms of defect density presented in the film. Supported by FAME (sponsored by MARCO and DARPA, Contract 2013-MA-2382), WV Higher Education Policy Commission Grant (HEPC.dsr.12.29), and WVU SRF. We also thank S. Kramer from Micron for providing the TiN-coated Si substrates.

  12. Process for Smoothing an Si Substrate after Etching of SiO2

    NASA Technical Reports Server (NTRS)

    Turner, Tasha; Wu, Chi

    2003-01-01

    A reactive-ion etching (RIE) process for smoothing a silicon substrate has been devised. The process is especially useful for smoothing those silicon areas that have been exposed by etching a pattern of holes in a layer of silicon dioxide that covers the substrate. Applications in which one could utilize smooth silicon surfaces like those produced by this process include fabrication of optical waveguides, epitaxial deposition of silicon on selected areas of silicon substrates, and preparation of silicon substrates for deposition of adherent metal layers. During etching away of a layer of SiO2 that covers an Si substrate, a polymer becomes deposited on the substrate, and the substrate surface becomes rough (roughness height approximately equal to 50 nm) as a result of over-etching or of deposition of the polymer. While it is possible to smooth a silicon substrate by wet chemical etching, the undesired consequences of wet chemical etching can include compromising the integrity of the SiO2 sidewalls and undercutting of the adjacent areas of the silicon dioxide that are meant to be left intact. The present RIE process results in anisotropic etching that removes the polymer and reduces height of roughness of the silicon substrate to less than 10 nm while leaving the SiO2 sidewalls intact and vertical. Control over substrate versus sidewall etching (in particular, preferential etching of the substrate) is achieved through selection of process parameters, including gas flow, power, and pressure. Such control is not uniformly and repeatably achievable in wet chemical etching. The recipe for the present RIE process is the following: Etch 1 - A mixture of CF4 and O2 gases flowing at rates of 25 to 75 and 75 to 125 standard cubic centimeters per minute (stdcm3/min), respectively; power between 44 and 55 W; and pressure between 45 and 55 mtorr (between 6.0 and 7.3 Pa). The etch rate lies between approximately equal to 3 and approximately equal to 6 nm/minute. Etch 2 - O2 gas flowing at 75 to 125 stdcm3/min, power between 44 and 55 W, and pressure between 50 and 100 mtorr (between 6.7 and 13.3 Pa).

  13. Nanoporous SiO2/TiO2 coating with enhanced interfacial compatibility for orthopedic applications

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaobing; Cao, Hengchun; You, Jing; Cheng, Xingbao; Xie, Youtao; Cao, Huiliang; Liu, Xuanyong

    2015-11-01

    Topographic modification in nanoscale is one of the most often used strategies to enhance the interfacial biocompatibility of implant materials. The aim of this work is to produce SiO2/TiO2 coatings with nanoporous structures and favorable biological properties by atmospheric plasma spraying technology and subsequently hydrothermal etching method in hydrogen fluoride solution. The effects of hydrothermal time and temperature on the microstructures and osteoblast behavior of the SiO2/TiO2 coatings were investigated. Results demonstrated that the as-sprayed SiO2/TiO2 coating was mainly composed of rutile and quartz phases. After etching, nanoporous topographies were formed on the surface of the coatings and the hydrothermal parameters had important influences on the size and shape of the pores. The interconnected network pores on the coating surface could only produce at the appropriate hydrothermal conditions (the hydrothermal time and temperature were 60 min and 100 °C, respectively). Compared to TiO2 and SiO2/TiO2 coatings, nanoporous SiO2/TiO2 coatings could enhance osteoblast adhesion and promote cell proliferation. The results suggested the potential application of the porous coatings for enhancing the biological performance of the currently used dental and orthopedic implant materials.

  14. Impact of Amorphous SiO2 Nanoparticles on a Living Organism: Morphological, Behavioral, and Molecular Biology Implications.

    PubMed

    Ambrosone, Alfredo; Scotto di Vettimo, Maria Rosaria; Malvindi, Maria Ada; Roopin, Modi; Levy, Oren; Marchesano, Valentina; Pompa, Pier Paolo; Tortiglione, Claudia; Tino, Angela

    2014-01-01

    It is generally accepted that silica (SiO2) is not toxic. But the increasing use of silica nanoparticles (SiO2NPs) in many different industrial fields has prompted the careful investigation of their toxicity in biological systems. In this report, we describe the effects elicited by SiO2NPs on animal and cell physiology. Stable and monodisperse amorphous silica nanoparticles, 25 nM in diameter, were administered to living Hydra vulgaris (Cnidaria). The dose-related effects were defined by morphological and behavioral assays. The results revealed an all-or-nothing lethal toxicity with a rather high threshold (35 nM NPs) and a LT50 of 38 h. At sub lethal doses, the morphophysiological effects included: animal morphology alterations, paralysis of the gastric region, disorganization and depletion of tentacle specialized cells, increase of apoptotic and collapsed cells, and reduction of the epithelial cell proliferation rate. Transcriptome analysis (RNAseq) revealed 45 differentially expressed genes, mostly involved in stress response and cuticle renovation. Our results show that Hydra reacts to SiO2NPs, is able to rebalance the animal homeostasis up to a relatively high doses of SiO2NPs, and that the physiological modifications are transduced to gene expression modulation.

  15. Impact of Amorphous SiO2 Nanoparticles on a Living Organism: Morphological, Behavioral, and Molecular Biology Implications

    PubMed Central

    Ambrosone, Alfredo; Scotto di Vettimo, Maria Rosaria; Malvindi, Maria Ada; Roopin, Modi; Levy, Oren; Marchesano, Valentina; Pompa, Pier Paolo; Tortiglione, Claudia; Tino, Angela

    2014-01-01

    It is generally accepted that silica (SiO2) is not toxic. But the increasing use of silica nanoparticles (SiO2NPs) in many different industrial fields has prompted the careful investigation of their toxicity in biological systems. In this report, we describe the effects elicited by SiO2NPs on animal and cell physiology. Stable and monodisperse amorphous silica nanoparticles, 25 nM in diameter, were administered to living Hydra vulgaris (Cnidaria). The dose-related effects were defined by morphological and behavioral assays. The results revealed an all-or-nothing lethal toxicity with a rather high threshold (35 nM NPs) and a LT50 of 38 h. At sub lethal doses, the morphophysiological effects included: animal morphology alterations, paralysis of the gastric region, disorganization and depletion of tentacle specialized cells, increase of apoptotic and collapsed cells, and reduction of the epithelial cell proliferation rate. Transcriptome analysis (RNAseq) revealed 45 differentially expressed genes, mostly involved in stress response and cuticle renovation. Our results show that Hydra reacts to SiO2NPs, is able to rebalance the animal homeostasis up to a relatively high doses of SiO2NPs, and that the physiological modifications are transduced to gene expression modulation. PMID:25325055

  16. Effect of Oxidation and SiO2 Coating on the Bonding Strength of Ti-Porcelain

    NASA Astrophysics Data System (ADS)

    Guo, Litong; Liu, Xiaochen; Zhu, Yabo; Xu, Cheng; Gao, Jiqiang; Guo, Tianwen

    2010-11-01

    Investigations on the effect of oxidation on titanium-ceramic adhesion were performed. Cast pure titanium was subjected to surface modification by preoxidation and introduction of an intermediate layer of SiO2 by sol-gel process. Specimens were characterized by TG-DSC, XRD, and SEM/EDS. The adhesion between the titanium and porcelain was evaluated by three-point flexure bond test. Failure of the titanium-porcelain with preoxidation treatment predominantly occurred at the titanium-oxide interface. Preoxidation treatment did not affect the fracture mode of the titanium-ceramic system and did not increase the bonding strength of Ti-porcelain. The SEM results revealed the existence of microcracks on the SiO2 coating surface oxidized at 800 °C in an air furnace. During the porcelain fusion, minute amounts of oxygen were able to penetrate the cracks and caused localized oxidation of the Ti-substrate. Failure of the titanium-porcelain with SiO2 coating predominantly occurred at the SiO2 layer. The SiO2 coating served as an effective oxygen diffusion barrier and improved the mechanical and chemical bonding between porcelain and titanium.

  17. A role of low pressure plasma discharge on etch rate of SiO2 dummy wafer

    NASA Astrophysics Data System (ADS)

    Milosavljevic, Vladimir; Zekic, Andrjana; Popovic, Dusan; Macgearailt, Niall; Daniels, Stephen

    2009-10-01

    Plasma has become indispensable for advanced materials processing, also low--k materials as SiO2 play important role in semiconductor industry. In this work a treatment of SiO2 single crystal by DC plasma discharge is studied in details. There are many effects occurred during plasma--surface interactions. Our work is focused on interaction between ions and dielectric surface. The etch rates, surface morphology and chemical composition of modified surface layer obtained by DC plasma etching are reported. Influence of plasma chemistry (SF6, O2, N2, Ar and He), discharge voltage (up to 1.2 kV), gas flow (up to 25 sccm, for each gas) and electrode--wafer geometry on etch rate of SiO2 wafer have been studied. Offline metrology is conducted for SiO2 wafer by SEM/EDAX technique and Raman scattering. Broad Raman peak at around 2800 cm-1 is observed for both, treated and original, investigated SiO2 wafers. Effects of plasma treatment conditions on integrated intensity of this peak are reported in the paper. An analysis of this correlation could be a framework for creating virtual etches rate sensors, which might be of importance in managing of plasma etching processes.

  18. Interaction of cesium adatoms with free-standing graphene and graphene-veiled SiO2 surfaces

    DOE PAGES

    Weck, Philippe F.; Kim, Eunja; Biedermann, Grant W.

    2015-04-21

    In this study, the interaction of Cs adatoms with mono- or bi-layered graphene (MLG and BLG), either free-standing or on a SiO2 substrate, was investigated using density functional theory. The most stable adsorption sites for Cs are found to be hollow sites on both graphene sheets and graphene-veiled SiO2(0001). In addition, larger dipole moments are created when a MLG-veiled SiO2(0001) substrate is used for adsorption of Cs atoms compared to the adsorption on free-standing MLG, due to charge transfer occurring between the MLG and the SiO2 substrate. For the adsorption of Cs on BLG-veiled SiO2(0001) substrate, these differences are smoothedmore » out and the binding energies corresponding to different sites are nearly degenerate; smaller dipole moments created by the Cs adatoms on BLG compared to MLG are also predicted.« less

  19. Genomic and functional analysis of Vibrio phage SIO-2 reveals novel insights into ecology and evolution of marine siphoviruses

    PubMed Central

    Baudoux, A-C.; Hendrix, R.W.; Lander, G.C.; Bailly, X.; Podell, S.; Paillard, C.; Johnson, J.E.; Potter, C.S.; Carragher, B.; Azam, F.

    2011-01-01

    We report on a genomic and functional analysis of a novel marine siphovirus, the Vibrio phage SIO-2. This phage is lytic for related Vibrio species of great ecological interest including the broadly antagonistic bacterium Vibrio sp. SWAT3 as well as notable members of the Harveyi clade (V. harveyi ATTC BAA-1116 and V. campbellii ATCC 25920). Vibrio phage SIO-2 has a circularly permuted genome of 80,598 bp, which displays unusual features. This genome is larger than that of most known siphoviruses and only 38 of the 116 predicted proteins had homologues in databases. Another divergence is manifest by the origin of core genes, most of which share robust similarities with unrelated viruses and bacteria spanning a wide range of phyla. These core genes are arranged in the same order as in most bacteriophages but they are unusually interspaced at two places with insertions of DNA comprising a high density of uncharacterized genes. The acquisition of these DNA inserts is associated with morphological variation of SIO-2 capsid, which assembles as a large (80 nm) shell with a novel T=12 symmetry. These atypical structural features confer on SIO-2 a remarkable stability to a variety of physical, chemical and environmental factors. Given this high level of functional and genomic novelty, SIO-2 emerges as a model of considerable interest in ecological and evolutionary studies. PMID:22225728

  20. Copper-vapor-assisted chemical vapor deposition for high-quality and metal-free single-layer graphene on amorphous SiO2 substrate.

    PubMed

    Kim, Hyungki; Song, Intek; Park, Chibeom; Son, Minhyeok; Hong, Misun; Kim, Youngwook; Kim, Jun Sung; Shin, Hyun-Joon; Baik, Jaeyoon; Choi, Hee Cheul

    2013-08-27

    We report that high-quality single-layer graphene (SLG) has been successfully synthesized directly on various dielectric substrates including amorphous SiO2/Si by a Cu-vapor-assisted chemical vapor deposition (CVD) process. The Cu vapors produced by the sublimation of Cu foil that is suspended above target substrates without physical contact catalyze the pyrolysis of methane gas and assist nucleation of graphene on the substrates. Raman spectra and mapping images reveal that the graphene formed on a SiO2/Si substrate is almost defect-free and homogeneous single layer. The overall quality of graphene grown by Cu-vapor-assisted CVD is comparable to that of the graphene grown by regular metal-catalyzed CVD on a Cu foil. While Cu vapor induces the nucleation and growth of SLG on an amorphous substrate, the resulting SLG is confirmed to be Cu-free by synchrotron X-ray photoelectron spectroscopy. The SLG grown by Cu-vapor-assisted CVD is fabricated into field effect transistor devices without transfer steps that are generally required when SLG is grown by regular CVD process on metal catalyst substrates. This method has overcome two important hurdles previously present when the catalyst-free CVD process is used for the growth of SLG on fused quartz and hexagonal boron nitride substrates, that is, high degree of structural defects and limited size of resulting graphene, respectively.