Optical emission characteristics of medium- to high-pressure N-2 dielectric barrier discharge plasmas during surface modification of polymers

National Science Foundation [NSF-20803007, NSF-10875025]The authors measured the band spectra (first and second positive systems) of the nitrogen molecule by optical emission spectroscopy with an aim to understand the mechanism of surface processing by medium- to high-pressure dielectric barrier discharge (DBD) plasmas. The experimentally measured and calculated spectra were compared to determine the vibrational and rotational temperatures of the N-2 (C-3 Pi(u)) state in the generated plasmas. The authors generated the N-2 DBD plasmas at a driving frequency of 1-7 kHz and a discharge pressure of 20-10(5) Pa for the surface modification of a polyethylene terephthalate (PET) sample. It was found that the vibrational temperature was greatly affected by the N-2 pressure while the rotational temperature remained constant in the N2 pressure range of 20-10(5) Pa. The emission intensity of N-2 first positive system (B-3 Pi -> A(3)Sigma) rapidly decreased at an increasing N-2 pressure due to the collisional relaxation process of the B-3 Pi state with N-2 molecules. The N-2(+)(B-2 Sigma(+)(u) -> X-2 Sigma(+)(g)) radiative transition was observed in the low-pressure DBD plasmas, which was attributed to the direct electron impact ionization of N-2 molecules. The surface characterizations of treated PET samples by contact angle measurement and atomic force microscopy indicate that the low-pressure N-2 DBD plasma is an effective method for the surface modification of polymers. Analysis indicates the plasma characteristics such as electron temperature and ion energy are mainly dependent on the N-2 pressure, which turn to determine the surface properties of treated PET samples. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3635372

Deposition of Large-Area and Protective Diamond-like Carbon Coatings on Glass Substrates by Low-Pressure Dielectric Barrier Discharges

Large-area (370mm x 500mm) diamond-like carbon (DLC) films were deposited on the glass substrate by low-pressure dielectric barrier discharges. The deposited DLC films were hard, homogeneous and extremely smooth. The DLC film deposited on the large-area glass can be potentially used as a scratch resistant and corrosion barrier layer.National Natural Science Foundation of China [10875025, 20803007

Electrospinning Hetero-Nanofibers In2O3/SnO2 of Homotype Heterojunction with High Gas Sensing Activity

In2O3/SnO2 composite hetero-nanofibers were synthesized by an electrospinning technique for detecting indoor volatile organic gases. The physical and chemical properties of In2O3/SnO2 hetero-nanofibers were characterized and analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), Energy Dispersive X-Ray Spectroscopy (EDX), specific surface Brunauer–Emmett–Teller (BET) and X-ray photoelectron spectroscopy (XPS). Gas sensing properties of In2O3/SnO2 composite hetero-nanofibers were measured with six kinds of indoor volatile organic gases in concentration range of 0.5~50 ppm at the operating temperature of 275 °C. The In2O3/SnO2 composite hetero-nanofibers sensor exhibited good formaldehyde sensing properties, which would be attributed to the formation of n-n homotype heterojunction in the In2O3/SnO2 composite hetero-nanofibers. Finally, the sensing mechanism of the In2O3/SnO2 composite hetero-nanofibers was analyzed based on the energy-band principle

Improved crystalline quality and light output power of GaN-based light-emitting diodes grown on Si substrate by buffer optimization

High-quality crack-free GaN-based light-emitting diodes (LEDs) were grown on patterned Si substrate using a flow modulation method and a high-temperature (HT)-AlN/AlGaN superlattice structure (SLs) interlayer. The effects of these two techniques on material properties and device performance were studied. The enhanced crystalline quality can be attributed to a 3D to 2D coalescence process with fewer dislocations initiated from the interlayers. The light output power of blue LEDs was improved by 66% after successful implementation of flow modulation and new interlayers. After substrate removal and packaging, the optical power of circle LEDs with diameter of 300 μm could reach as high as 6.30 mW at 20 mA

Economical and effective sulfide catalysts for dye-sensitized solar cells as counter electrodes

Molybdenum sulfide (MoS2) and tungsten sulfide (WS2) are proposed as counter electrode (CE) catalysts in a I3-/I- and T2/T- based dye-sensitized solar cells (DSCs) system. The I3-/I- based DSCs using MoS2 and WS2 CEs achieved power conversion efficiencies of 7.59% and 7.73%, resp