Optical and surface properties of hybrid TiO2/ormosil planar waveguide prepared by the sol-gel process

Two kinds of silanes, 3-glycidoxypropyltrimethoxysilane (GLYMO) and 3-trimethoxysililpropylmethacrylate (TMSPM), were used to prepare ormosil waveguide films by the sol-gel method. Thirty percent Ti(OBu)(4) and 70% silane were contained in the precursor sets. The properties of films were measured by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), UV/VIS/NIR spectrophotometer (UV-vis), atomic force microscopy (AFM), m-line and scattering-detection method. The films from GLYMO and TMSPM precursors exhibit similar thickness (2.58 mu m for GLYMO, 2.51 mu m for TMSPM) and refractive index (1.5438 for GLYMO, 1.5392 for TMSPM, lambda=632.8 nm), but the film from TMSPM precursor has higher propagation loss (1.024 dB/cm, lambda=632.8 nm) than the film prepared from GLYMO (0.569 dB/cm, lambda=632.8 nm). Furthermore, the film prepared from TMSPM is easy to be opaque and cracks during coating whereas the same phenomenon was not found for the film prepared with GLYMO. It is confirmed that GLYMO is a better precursor than TMSPM for waveguide film preparation. (C) 2005 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Efeito da temperatura de secagem de dois tipos de silano e da supressão ou redução do tempo de condicionamento com ácido hidrofluorídrico na resistência de união entre uma cerâmica de dissilicato de lítio e um cimento resinoso

Este estudo avaliou o efeito de diferentes métodos de silanização e aplicação do ácido hidrofluorídrico (HF) sobre a resistência à microtração de uma cerâmica de dissilicato de lítio a um cimento resinoso. Quarenta blocos de IPS e.max Press /Ivoclar Vivadent (5x5x6mm) foram cimentados a blocos de resina Z250/3M ESPE (5x5x6mm) usando o cimento resinoso RelyX ARC/3M ESPE de acordo com os seguintes métodos de tratamento superficial: G1: 20s de ácido fluorídrico (HF) + silano não hidrolisado Primer-Activactor/Dentsply (SNH) seco à temperatura ambiente; G2: 20s HF + silano pré-hidrolisado RelyX Ceramic-Primer/3M ESPE (SPH) seco à temperatura ambiente; G3: 10s HF + SNH seco com ar quente (50oC-2min); G4: 10sHF + SPH seco com ar quente (50oC-2min); G5: sem ácido, SNH seco com ar quente (50oC-2min); G6: sem ácido, SPH seco com ar quente (50oC-2min); G7: sem ácido, SNH seco à temperatura ambiente; G8: sem ácido, SPH seco à temperatura ambiente. Antes de cada método de silanização, os blocos cerâmicos receberam acabamento com lixas de carbeto de silício (220-600) e limpeza com ácido fosfórico 37% (1min). A cimentação foi realizada com carga vertical de 1kg por 10min. Os conjuntos de cerâmica/cimento/resina foram armazenados em água destilada (37C) por 24 horas e depois seccionados em máquina de corte Isomet 1000 a fim de obter palitos (n = 40) de 1mm2 de área da seção transversal, que foram submetidos ao teste de microtração em máquina de ensaio universal Emic (v = 0,5mm/min). O modo de fratura foi avaliado em microscópio eletrônico de varredura. A análise estatística foi realizada utilizando ANOVA / Dunnett (p-valor = 0,000). As médias MPa e desvio padrão foram: G1-21,5 (8,9) BC; G2-30,5 (7,2) A; G3-19.4 (9.1) BC; G4-24,0 (9,0) B; G5-8.1 (3.2) D; G6 -18,0 (6,2) C; G7-7.8 (2,6) D; G8-6.3 (2,5) D. Grupos 2, 3, 4 e 6 não tiveram falhas prematuras dos palitos contra os grupos 1, 5, 7 e 8, que apresentaram 2,2; 44,4; 75,6 e 33,3% de perdas prematuras, respectivamente. O teste de correlação foi realizado apresentando significância estatística, com valor de -0,736 (p-valor = 0,000), mostrando que, a medida que o percentual de perda prematura aumenta, a média da MPa diminui. Quanto ao modo de fratura, observou-se 44,97% de falhas do tipo mista, 51,70% de falhas do tipo adesiva, 3,33% de falhas do tipo coesiva do cimento. Quando é realizada a supressão do condicionamento com HF como pré-tratamento da superfície cerâmica IPS e.max Press, a aplicação de silano SPH, associada ao seu tratamento térmico, deve ser o método de silanização recomendado, embora os valores mais elevados de resistência de união tenham sido os obtidos quando utilizado o condicionamento com HF por 20s. Quando é realizada a redução do tempo de condicionamento com HF para 10s, a aplicação do silano (SPH ou SNH) deve ser sempre associada ao seu tratamento térmico. O SNH só deve ser usado se as superfícies das cerâmicas IPS e.max Press forem tratadas com HF.

Processos de formação de ligações cruzadas de polietileno de alto peso molecular

No projeto desenvolvido, ligações cruzadas foram formadas no polietileno de alta densidade e alto peso molecular, grade HS5103, através dos processos reticulação por peróxidos e silanos, com o objetivo de se avaliar o efeito da introdução de ligações cruzadas nas propriedades térmicas e mecânicas deste PEAD. Misturas entre o HS5103 e os peróxidos orgânicos, 2,5-Dimetil-2,5-di(terc-butilperoxi)hexano (DHBP) e peróxido de dicumila (DCP), foram produzidas e analisadas para a avaliação do efeito dos tipos de peróxido na reticulação e propriedades do PEAD e para determinação da concentração e do tipo de peróxido a ser utilizado como agente iniciador de reticulação por silano. Ensaios de índice de fluidez (MFI), reometria capilar, extração de polímero por xileno (teor de gel), análise termogravimétrica (TGA), calorimetria diferencial de varredura (DSC) e tração foram realizados para caracterização das misturas com peróxidos. Os resultados indicaram aumento da viscosidade com o aumento da concentração de peróxido, sendo o DHBP o que apresentou maior índice de aumento; não houve mudanças relevantes nas propriedades mecânicas e, ocorreu aumento do grau de cristalinidade, sendo mais significativo nas amostras com DCP. Após avaliação dos resultados citados, para as amostras a serem reticuladas via silano, foi promovida a graftização de diferentes concentrações de viniltrimetóxisilano (VTMS) na presença de 0,01%p/p de DCP com a adição de 0,05%p/p de catalisador, posteriormente a reticulação foi promovida em água. As amostras produzidas foram caracterizadas por ensaios de teor de gel, análise dinâmico-mecânica (DMA), espectroscopia de absorção no infravermelho (FTIR), TGA, ensaios de desgaste por deslizamento e tração. Nas amostras com silano a formação de ligações cruzadas foi gradativa, apresentando de 8% de gel para amostra com 0,5%p/p de VTMS a 57 % para amostra com1,5% p/p de silano, maior concentração utilizada. A análise dinâmico-mecânica (DMA) realizada evidenciou que houve um aumento densidade de ligações cruzadas e do módulo de armazenamento após temperatura de fusão com o teor de silano, concordando com os resultados de teor de gel. As análises de FTIR mostraram que houve a graftização e a formação de ligações cruzadas no PEAD HS5103. Não se observou um aumento significativo para o limite de resistência para o PEAD modificado. E os testes de desgaste por deslizamento indicaram um aumento da resistência ao desgaste das amostras reagidas com VTMS.

Hydrogenated amorphous silicon and silicon nitride deposited at less than 100° C by ECR-PECVD for thin film transistors

A systematic study has been made of the growth of both hydrogenated amorphous silicon (a-Si:H) and silicon nitride (a-SiN) by electron cyclotron resonance plasma enhanced chemical vapour deposition (ECR-PECVD). In the case of a-SiN, helium and nitrogen gas is injected into the system such that it passes through the resonance zone. These highly ionised gases provide sufficient energy to ionise the silane gas, which is injected further downstream. It is demonstrated that a gas phase reaction occurs between the silane and nitrogen species. It is control of the ratio of silane to nitrogen in the plasma which is critical for the production of stoichiometric a-SiN. Material has been produced at 80°C with a Si:N ratio of 1:1.3 a breakdown strength of ∼6 MV cm-1 and resistivity of > 1014 Ω cm. In the case of a-Si:H, helium and hydrogen gas is injected into the ECR zone and silane is injected downstream. It is shown that control of the gas phase reactions is critical in this process also. a-Si:H has been deposited at 80 °C with a dark conductivity of 10-11 Ω-1 cm-1 and a photosensitivity of justbelowl 4×104. Such materials are suitable for use in thin film transistors on plastic substrates.

Microwave power effects on the properties of phosphorus-doped SiC:H films prepared using ECR-CVD

There has been a growing interest in hydrogenated silicon carbide films (SiC:H) prepared using the electron cyclotron resonance-chemical vapour deposition (ECR-CVD) technique. Using the ECR-CVD technique, SiC:H films have been prepared from a mixture of methane, silane and hydrogen, with phosphine as the doping gas. The effects of changes in the microwave power (from 150 to 900 W) on the film properties were investigated in a series of phosphorus-doped SiC:H films. In particular, the changes in the deposition rate, optical bandgap, activation energy and conductivity were investigated in conjunction with results from Raman scattering and Fourier transform infra-red (FTIR) analysis. It was found that increase in the microwave power has the effect of enhancing the formation of the silicon microcrystalline phase in the amorphous matrix of the SiC:H films. This occurs in correspondence to a rapid increase in the conductivity and a reduction in the activation energy, both of which exhibit small variations in samples deposited at microwave powers exceeding 500 W. Analysis of IR absorption results suggests that hydrogen is bonded to silicon in the Si-H stretching mode and to carbon in the sp3 CHn rocking/wagging and bending mode in films deposited at higher microwave powers.

A microbeam RBS analysis of low temperature direct-write inkjet deposited copper

Quantitative microbeam Rutherford backscattering (RBS) analysis with a 1.5 MeV 4He+ beam has determined limits on the purity of copper deposited on glass with a novel inkjet process. A tetravinyl silane tetrakisCu(I) 1,1,1,5,5,5-hexafluoroacetylacetonate (TVST[Cu]hfac) complex was heated to 70 °C and jetted onto the glass substrate through a piezoelectric ceramic print head in droplets about 0.5 mm diameter. The substrate temperature was 150 °C. Solid well-formed deposits resulted which have a copper content greater than about 90% by weight. The RBS spectra were analysed objectively using the DataFurnace code, with the assumption that the deposit was CuOx, and the validity of different assumed values of x being tested. The assumptions and the errors of the analysis are critically evaluated. © 2002 Elsevier Science B.V. All rights reserved.

Peculiarity of constant photocurrent method for silicon films with mixed amorphous-nanocrystalline structure

The results of conductivity, photoconductivity and constant photocurrent method absorption measurements by DC and AC methods in hydrogenated silicon films with mixed amorphous-nanocrystalline structure are presented. A series of diphasic silicon films was deposited by very high frequency plasma enhanced chemical vapor deposition technique, using different hydrogen dilution ratios of silane. The increase of hydrogen dilution ratio results in five orders of magnitude increase of conductivity and a sharp increase of grain volume fraction. The comparison of the absorption spectra obtained by DC and AC methods showed that they are similar for silicon films with the predominantly amorphous structure and films with high grain volume fraction. However we found a dramatic discrepancy between the absorption spectra obtained by DC and AC constant photocurrent methods in silicon films deposited in the regime of the structure transition from amorphous to nanocrystalline state. AC constant photocurrent method gives higher absorption coefficient than DC constant photocurrent method in the photon energy range of 1.2-1.7 eV. This result indicates the possibility of crystalline grains contribution to absorption spectra measured by AC constant photocurrent method in silicon films with intermediate crystalline grain volume fraction. (c) 2008 Published by Elsevier B.V.

Impacts of hydrogen dilution on growth and optical properties of a-SiC : H films

Hydrogenated amorphous silicon-carbon (a-SiC:H) films were deposited by plasma enhanced chemical vapor deposition (PECVD) with a fixed methane to silane ratio ([CH4]/[SiH4]) of 1.2 and a wide range of hydrogen dilution (R-H=[H-2]/[SiH4 + CH4]) values of 12, 22, 33, 102 and 135. The impacts of RH on the structural and optical properties of the films were investigated by using UV-VIS transmission, Fourier transform infrared (FTIR) absorption, Raman scattering and photoluminescence (PL) measurements. The effects of high temperature annealing on the films were also probed. It is found that with increasing hydrogen dilution, the optical band gap increases, and the PL peak blueshifts from similar to1.43 to 1.62 eV. In annealed state, the room temperature PL peak for the low R-H samples disappears, while the PL peak for the high R-H samples appears at similar to 2.08 eV, which is attributed to nanocrystalline Si particles confined by Si-C and Si-O bonds.

The diphasic nc-Si/a-Si : H thin film with improved medium-range order

A series of silicon film samples were prepared by plasma enhanced chemical vapor deposition (PECVD) near the threshold from amorphous to nanocrystalline state by adjusting the plasma parameters and properly increasing the reactions between the hydrogen plasma and the growing surface. The microstucture of the films was studied by micro-Raman and Fourier transform infrared (FTIR) spectroscopy. The influences of the hydrogen dilution ratio of silane (R-H = [H-2]/[SiH4]) and the substrate temperature (T-s) on the microstructural and photoelectronic properties of silicon films were investigated in detail. With the increase of RH from 10 to 100, a notable improvement in the medium-range order (MRO) of the films was observed, and then the phase transition from amorphous to nanocrystalline phase occurred, which lead to the formation of diatomic hydrogen complex, H-2* and their congeries. With the increase of T-s from 150 to 275 degreesC, both the short-range order and the medium range order of the silicon films are obviously improved. The photoconductivity spectra and the light induced changes of the films show that the diphasic nc-Si/a-Si:H films with fine medium-range order present a broader light spectral response range in the longer wavelength and a lower degradation upon illumination than conventional a-Si:H films. (C) 2004 Elsevier B.V. All rights reserved.

Preferred growth of nanocrystalline silicon in boron-doped nc-Si : H Films

Preferred growth of nanocrystalline silicon (nc-Si) was first found in boron-doped hydrogenated nanocrystalline (nc-Si:H) films prepared using plasma-enhanced chemical vapor deposition system. The films were characterized by high-resolution transmission electron microscope, X-ray diffraction (XRD) spectrum and Raman Scattering spectrum. The results showed that the diffraction peaks in XRD spectrum were at 2theta approximate to 47degrees and the exponent of crystalline plane of nc-Si in the film was (220). A considerable reason was electric field derived from dc bias made the bonds of Si-Si array according to a certain orient. The size and crystalline volume fraction of nc-Si in boron-doped films were intensively depended on the deposited parameters: diborane (B2H6) doping ratio in silane (SiH4), silane dilution ratio in hydrogen (H-2), rf power density, substrate's temperature and reactive pressure, respectively. But preferred growth of nc-Si in the boron-doped nc-Si:H films cannot be obtained by changing these parameters. (C) 2004 Elsevier Ltd. All rights reserved.

Characterization of silicon carbide thin films and their use in colour sensor

A series of hydrogenated amorphous silicon carbide (a-Si1-xCx:H) films were prepared by plasma-enhanced chemical vapour deposition (PECVD) using a gas mixture of silane, methane, and hydrogen as the reactive source. The previous results show that a high excitation frequency, together with a high hydrogen dilution ratio of the reactive gases, allow an easier incorporation of the carbon atoms into the silicon-rich a-Si1-xCx:H film, widen the valence controllability. The data show that films with optical gaps ranging from about 1.9 to 3.6 eV could be produced. In this work the influence of the hydrogen dilution ratio of the reactive gases on the a-Si1-xCx:H film properties was investigated. The microstuctural and photoelectronic properties of the silicon carbide films were characterized by Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), and FT-IR spectrometry. The results show that a higher hydrogen dilution ratio enhances the incorporation of silicon atoms in the amorphous carbon matrix for carbon-rich a-Si1-xCx:H films. One pin structure was prepared by using the a-Si1-xCx:H film as the intrinsic layer. The light spectral response shows that this structure fits the requirement for the top junction of colour sensor. (c) 2004 Elsevier B.V. All rights reserved.

Boron-doped silicon nanowires grown by plasma-enhanced chemical vapor deposition

Boron-doped ( B-doped) silicon nanowires have been successfully synthesized by plasma-enhanced chemical vapor deposition (PECVD) at 440degreesC using silane as the Si source, diborane( B2H6) as the dopant gas and An as the catalyst. It is desirable to extend this technique to the growth of silicon nanowire pn junctions because PECVD enables immense chemical reactivity.

Light-induced changes in diphasic nanocrystalline silicon films and solar cells

A series of diphasic nanocrystalline silicon films and solar cells was prepared using different hydrogen dilution ratios of silane by very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD). It was observed that after light soaking the open circuit voltage (V-oc) of the diphasic solar cells increased, while that of amorphous silicon solar cells decreased. Raman scattering spectroscopy was performed on the series of diphasic silicon films before and after light soaking. It was found that after light soaking the nanostruclures in the diphasic nanocrystalline silicon films were changed. Both the grain sizes and grain volume fraction reduced, while the grain boundary components increased. These results provide experimental evidence for the conjecture that the light-induced increase in V-oc of the diphasic nanocrystalline solar cells might be induced by the changes in the nanostructure of the intrinsic layer. (c) 2006 Elsevier B.V. All rights reserved.

The study of high temperature annealing of a-SiC : H films

A series of amorphous silicon carbide films were prepared by plasma enhanced chemical vapor deposition technique on (100) silicon wafers by using methane, silane, and hydrogen as reactive resources. A very thin (around 15 A) gold film was evaporated on the half area of the aSiC:H films to investigate the metal induced crystallization effect. Then the a-SiC:H films were annealed at 1100 degrees C for 1 hour in the nitrogen atmosphere. Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to analyze the microstructure, composition and surface morphology of the films. The influences of the high temperature annealing on the microstructure of a-SiC:H film and the metal induced metallization were investigated.

Silicon nanowires grown on a pre-annealed Si substrate

Polycrystalline Si nanowires (poly SiNWS) were successfully synthesized by plasma-enhanced chemical vapor deposition (PECVD) at 440degreesC using silane as the Si source and Au as the catalyst. The diameters of Si nanowires range from 15 to 100nm. The growth process indicates that to fabricate SiNWS by PECVD, pre-annealing at high temperature is necessary. A few interesting nanowires with Au nanoclusters uniformly distributed in the body of the wire were also produced by this technique. (C) 2002 Elsevier Science B.V. All rights reserved.