Papers by Keyword: HMDS

Abstract: In this work, 3’-flouro-2,2',6,6'-tetraphenyl-4,4'-dipyranylidene (3FDP) was originally synthesized and investigated with density functional theory (DFT) calculations, ultraviolet–visible spectroscopy (UV–Vis) and cyclic voltammetry (CV) in comparison with 2,2',6,6'-tetraphenyl-4,4'-dipyranylidene (DP) and 4’-flouro-2,2',6,6'-tetraphenyl-4,4'-dipyranylidene (4FDP). 3FDP-based organic field-effect transistors (OFETs) were fabricated with bottom contact configuration on bare SiO₂/Si substrate, 1,1,1,3,3,3-hexamethyldisilazane (HMDS) and octadecyltrichlorosilane (OTS) treated substrate, respectively. The HMDS-treated device showed highest mobility of 4 × 10⁻⁴ cm² V⁻¹ s⁻¹, on/off ratio of 4 × 10³ and threshold voltage of −10 V. Finally, vacuum deposited 3FDP films morphology was investigated by X-ray diffraction (XRD) analyses and the results showed higher crystallinity of HMDS-treated 3FDP film compared to the OTS-treated film, leading to a better FET performance.

Abstract: Accident Tolerant fuel (ATF) concept was put forward after the Fukushima accident. Among different kinds of ATF, Fully Ceramic Microencapsulated Fuels (FCM) have been paid more and more attention in recent years. SiC matrix is one of the important constituent parts in FCM fuel system, which is sintered from kinds of SiC powders. In this study, SiC nanoparticles were prepared by Fluidized Bed Chemical Vapor Deposition (FB-CVD) method using Hexamethyldisilane (HMDS) as precursor, aimed at reducing the sintering temperature and pressure of FCM-SiC matrix. Experiments of different temperatures with different argon gas ratios were carried out. It was found that good crystal SiC could be obtained from 850°C to 1250°C, under pure hydrogen or H₂: Ar=15:1. Different H₂ carrier gas flow rate tests were also conducted. With the increase of hydrogen flow rates, the SiC was transformed from 3C-SiC to other types, such as 6H or 15R, but no significant effect was found on particle shape. Based on the characterizations of XRD, SEM and TEM, the results showed the spherical SiC nanoparticles could be obtained as well as 20 nanometers in diameter at the condition of 1150°C, H₂: Ar=15:1, under different hydrogen flow rates. Different hydrogen flow rates had little influence on the particle size of SiC nanoparticles.

Abstract: Tristructural-isotropic (TRISO) particle, with spherical ceramic fuel particle kernels followed by three layers of pyrolytic carbon and one layer of silicon carbide (SiC), has been successful now in high temperature gas cooled reactor (HTGR). The silicon carbide (SiC) layer used in TRISO coated fuel particles is normally produced at high temperatures (~1600°C) via fluidized bed chemical vapor deposition from methyltrichlorosilane (MTS) in a hydrogen environment. The precursor is strong corrosive and the process is not environmentally friendly. In this work, hexamethyldisilane (HMDS) was used instead of MTS and the deposition behavior was investigated via fluidized bed chemical vapor deposition method. Different experimental parameters were tested, such as deposition temperature (800~1450°C) and gas flow ratio of Ar: H₂. The deposition rates were obtained and compared. It was found that the optimization parameters of highest deposition rate is 1000°C with the ratio of Ar: H₂ of 1:1. The microstructures of the products were further investigated by SEM, XRD and Raman scattering. From the X-ray diffraction pattern it could be inferred that the β-SiC phase was obtained, and free carbon was also found in deposition products. Different types of SiC layer, including dense and porous layer can be prepared. The experimental results validated that HMDS was an alternative precursor for preparing the SiC layer in producing the TRISO particle and other SiC-coated materials in lower temperatures

Abstract: Antireflective coatings with stable hydrophobicity for solar tube were prepared via sol-gel method and hexamethyldisilazane (HMDS) treatment. The coatings have a high porosity, groove-like surface morphology and a big static water contact angle. As a result, the coatings exhibit high transmittance even in high humidity environments. The transmittance peak can reach up to 99.02% which increased by 7% compared with the substrate and the wavelength band increased by more than 5% is from 438nm to 1000nm. After prolonged exposure to strong ultraviolet (UV) irradiation, the static water contact angle of the HMDS treated antireflective coatings decreased very small from 102^o to 98^o. In addition, the low-temperature tests showed the contact angle did not decline even at-50°C. The results suggest that the coatings prepared in present paper have stable hydrophobic and antireflective performance in the environment of strong UV radiation and low temperature.

Abstract: The CVD growth of SiC thin films using hexamethyldisilane (HMDS) as the singular precursor on Si substrates with an AlN nucleation layer was explored in this study. A statistically designed experiment was used to conclude that growth temperature has the largest impact on crystal quality and surface microstructure. In addition to crystal quality, wafer bow was studied. Crystal quality and growth rate are loosely correlated to wafer bow in our study. SEM surface microstructural analysis of the SiC films shows a changing microstructure with growth temperature consistent changes in measured crystal quality. TEM studies reveal that the films are the 3C polytype having a high density of planar faults.

Abstract: We adopted HMDS(Hexamethyledisilane) as a SiC(Silicon carbide) source material for epitaxial growth of 3C-SiC on Si substrate. Various growth profiles were investigated to optimize hetero-epitaxial growth of 3C-SiC layers. We also focused on the homogeneous film deposition of 3C-SiC on Si by employing two susceptor shapes, flat and tilted susceptors, to control a thickness of the boundary layer formed on the Si substrate. Fringe color patterns were observed on 3C-SiC layer on Si and hence it was easy to characterize the film uniformity by analyzing this color. 3C-SiC epitaxial layers were systematically analyzed by an optical microscope, a Raman spectroscopy, a SEM and an XRD.

Abstract: This paper presents the Raman scattering characteristics of poly 3C-SiC thin films deposited on AlN buffer layer by atmospheric pressure chemical vapor deposition (APCVD) using hexamethyldisilane (MHDS) and carrier gases (Ar + H2). The Raman spectra of SiC films deposited on AlN layer of before and after annealings were investigated according to the growth temperature of 3C-SiC. Two strong Raman peaks, which means that poly 3C-SiC admixed with nanoparticle graphite, were measured in them. The biaxial stress of poly 3C-SiC/AlN was calculated as 896 MPa from the Raman shifts of 3C-SiC deposited at 1180 °C on AlN of after annealing.

Abstract: This paper describes the characteristics of poly (Polycrystalline) 3C-SiC grown on SiO2 and AlN buffers, respectively. The crystallinity and the bonding structure of poly 3C-SiC grown on each buffer layer were investigated according to various growth temperatures. The crystalline quality of poly 3C-SiC was improved from resulting in decrease of FWHM (Full width half maximum) of XRD and FT-IR by increasing the growth temperature. The minimum growth temperature of poly 3C-SiC was 1100 °C. The surface chemical composition and the electron mobility of poly 3C-SiC grown on each buffer layer were investigated by XPS and Hall Effect. The chemical compositions of surface of poly 3C-SiC grown on SiO2 and AlN were not different. However, their electron mobilities were 7.65 ㎝2/V.s and 14.8 ㎝2/V.s, respectively. Therefore, since the electron mobility of 3C-SiC/AlN was two times higher than that of 3C-SiC/SiO2, AlN is a suitable material, as buffer layer, for SiC growth with excellent crystalline quality.

Abstract: In this paper, we report a novel route to synthesize nano-sized cubic silicon carbide (3CSiC) powder by a chemical vapor deposition (CVD) technique in a resistance-heated furnace. The nanoparticles were deposited on the relatively cold region of a hot-wall quartz reactor. Hexamethyldisilane (HMDS) was used as the source material for both silicon and carbon. The presence of crystalline 3C-SiC was identified using powder x-ray diffraction (XRD) technique. From the XRD data, the crystallite size was also estimated to be in the range of nanometers (nm). A clear evidence of the particle size (~ 10 - 30 nm) was obtained by transmission electron microscopy (TEM). Selected area electron diffraction (SAED) was carried out on the nanoparticle assembly. The ring shaped pattern is a clear indication of polycrystalline particle formation. High resolution TEM (HRTEM) of nanoparticles was performed to study the crystal structure in detail. The nanoparticles were also characterized by Raman spectroscopy at room temperature. Finally, the influence of the growth parameters is also reported in the present study.

Abstract: Selective epitaxial growth (SEG) of cubic silicon carbide (3C-SiC) was carried out on patterned Si (100) substrates using SiO2 as a mask. The growth was performed by atmospheric pressure chemical vapour deposition in a resistance-heated furnace using hexamethyldisilane (HMDS) as the source. It was observed that voids are the major defect in the case of heteroepitaxial growth of 3C-SiC on Si. Using selective epitaxial growth, the density of voids was reduced. Lateral epitaxial overgrowth (LEO) was achieved at selected areas where windows are arrays of stripes. The effect of temperature, window shape and size, precursor concentration, etc. on the SEG of SiC has been studied. After growth, films have been characterized by Nomarski optical microscopy, SEM, Raman spectroscopy and AFM. Faceted growth was observed along (111) planes inside smaller windows. Raman spectroscopy was used to identify defects and the presence of other polytypes.