Surface acoustic wave reflection from diamond-like carbon thin film reflecting arrays on LiNbO3 substrates

Surface acoustic wave (SAW) reflection from diamond-like carbon (DLC) strip reflecting arrays on Y-Z LiNbO₃ is investigated. The reflection from DLC strips with triangular cross section has been observed. Reflection increases in alternating DLC and Al strips in 90° reflecting arrays in comparison with pure Al structures. The values of reflection coefficient per period in the slanted reflecting arrays are estimated to be about 1.0% for pure DLC strips (height to wavelength ratio equal to 0.02), 2% for uniform Al coating on DLC reflecting arrays, and 3.5% for alternating DLC and Al strips. This value is higher than that for pure Al strips by about 0.7%. Reflection properties are briefly discussed, and preparation technique is presented     

Design of field-plate terminated 4H-SiC Schottky diodes using high-k dielectrics

Silicon carbide (SiC) field-plate terminated Schottky diodes using silicon dioxide (SiO₂) dielectric experience high electric field in the insulator and premature dielectric breakdown, attributed to the lower dielectric constant of the oxide. To alleviate this problem we explore the use of high-k dielectrics, silicon nitride (Si₃N₄) and sapphire (Al₂O₃), on 4H-SiC by numerical simulations using Medici. The simulation results show significant improvement in blocking voltages by as much as 30% and much lower electric field within the dielectrics. There is also a slight reduction in the specific-on resistance (R_sp-on) and a small increase in the forward current density due to the formation of an accumulation layer in SiC where the metal overlaps the dielectric. This effect is enhanced with increasing dielectric constant and decreasing dielectric thickness for a given dielectric.     

Synthesis and Spectroscopic Studies of DGEBA–Grafted Polyaniline

N-grafted polyaniline with diglycidyl ether bisphenol A (DGEBA) was synthesized via anionic copolymerization technique. Metalation reaction was performed to cause grafting to occur between DGEBA with emeraldine salt polyaniline (PANI-ES) and leucoemeraldine base polyaniline (PANI-LEB), respectively. Fourier transform infrared (FTIR), ¹³C-nuclear magnetic resonance (NMR), and ¹H-NMR spectroscopies and gel permeation chromatography (GPC) were performed to characterize the PANI-EB-g-DGEBA and PANI-ES-g-DGEBA copolymers. The gel content of the resultant copolymers was determined by Soxhlet extraction. Results of spectroscopic studies showed that grafting took place together with the side reaction, cross-linking, and DGEBA homopolymerization. Oxidation states of PANI were found to influence the gel content and molecular weight distribution of copolymers produced.     

Surface roughness effect on optical loss in waveguide using isotropically induced crosslink network of siloxane–polyimide copolymer

Optical properties of two-fluorinated polysiloxane-co-polyimide (PI-PDMS and 3-(aminopropyl)triethoxysilane [PI-APTES]) were investigated based on their molecular structure and compared with the pure PI at 1,550 nm radiation. The refractive indexes and birefringence of the copolymers were reduced which is attributable to the chain flexibility as substantiated from the differential scanning calorimetry result. They are highly transparent at near infrared (NIR) region with light transmittance above 90% at visible region while displaying excellent thermal stability up to 456°C. Asymmetry planar waveguides was fabricated which recorded a respectable low optical loss 0.020 dB/cm for pure PI, 0.042 dB/cm for PI-PDMS, and 0.066 dB/cm for PI-APTES, respectively. Despite proving low NIR absorption and low birefringence, extrinsic factor namely surface roughness was accounted as affecting the higher optical loss in polyimide siloxane copolymer compared to pure PI. The excellent thermal and optical properties displayed by these series of material established their viable application as waveguide material at 1,550 nm wavelength.     

The influence of rf induced bias on the properties of diamond-like carbon films prepared using ECR-CVD

The deposition of diamond-like carbon (DLC) films from a mixture of hydrogen and methane using the electron resonance chemical vapor deposition (ECR-CVD) method with radio-frequency (rf) bias is reported. The structural characteristics of the DLC films were characterized using Raman spectroscopy. The effects of the self-generated dc bias resulting from the rf power on the optical gap, Raman spectra, infrared (IR) absorption, and film hardness in depositions carried out at 7 and 15 mTorr process pressures were investigated. Under conditions of 100 W microwave power and for dc bias variation ranging from −10 to −200 V, there is evidence from Raman scattering analysis to show an increase in the DLC-like characteristic in films deposited at low dc bias at both process pressures. The variation of the D and G line peak position and intergrated intensity ratio (I_D/I_G) in the Raman spectra correlates well with the film hardness profile. There does not seem to be a relationship between the variation of the C-H absorption peak intensity in the IR spectra (bonded hydrogen content) and the optical gap, although films with the highest optical gap tend to show a relatively higher C-H absorption peak intensity in the IR spectra. Films deposited at high dc bias showed a reduction in the C-H infrared absorption, suggesting a reduction in the bonded hydrogen content.     

High-efficiency si/polymer hybrid solar cells based on synergistic surface texturing of Si nanowires on pyramids

An efficient Si/PEDOT:PSS hybrid solar cell using synergistic surface texturing of Si nanowires (SiNWs) on pyramids is demonstrated. A power conversion efficiency (PCE) of 9.9% is achieved from the cells using the SiNW/pyramid binary structure, which is much higher than similar cells based on planar Si, pyramid-textured Si, and SiNWs. The PCE is the highest reported to-date for hybrid cells based on Si nanostructures and PEDOT.     

Determination of filler content in thermoplastic composites by FTIR analysis

FTIR quantitative analytical method is described as an alternative technique for computation of the filler content in polypropylene composites. White rice husk ash (WRHA) was incorporated as a filler material into polypropylene homopolymer. Absorption peaks at 480, 621, and 790 cm^?1 chosen for the quantitative analysis work have been shown to give good linearity with increasing filler contents. © 1995 John Wiley & Sons, Inc.     

Photoluminescence in amorphous carbon thin films and its relation to the microscopic properties

The photoluminescence properties of amorphous hydrogenated carbon (a-C:H) films grown using a r.f. plasma have been investigated. It is found that the photoluminescence (PL) spectra exhibit a red shift, accompanied by a sharp decrease in PL efficiency and an increase in electron spin density as the applied r.f. power increases. The results can be interpreted by a model in which the a-C:H films consist of two phases with π-bonded clusters embedded in an sp³-bonded amorphous matrix. The excitation and the recombination of electron hole pairs are believed to take place in the π-bonded clusters. As a result of the confinement effect of electron hole pairs in these clusters, the cluster size becomes an important parameter in understanding the PL properties of a-C:H films.     

Short Review on Sepiolite-Filled Polymer Nanocomposites

Latest developments in mineral clay nanocomposites area are reviewed in this report, with a specific focus on sepiolite clay mineral. Rigorous research has been conducted on the sepiolite clay mineral by both academicians and industrial researchers. The properties of the nanocomposites are significantly dependent on the polymer matrices, their nature, modification, and preparation technique. Thus, preparation, structure, and characteristics of polymer sepiolite nanocomposites are thoroughly discussed, in addition to the scientific literature to support and find any gaps for future research.