Szu-Hsueh Lai

Electron field emission from various morphologies of fluorinated amorphous carbon nanostructures

Unlike general fluorination, amorphous fluorinated carbon (a‐C:F) nanostructures have been synthesized directly and efficiently by an electron cyclotron resonance chemical vapor deposition (ECR–CVD) system using a mixture of C2H2, CF4, and Ar as precursors. The electron field-emission properties of the a‐C:F nanostructures were investigated. The a‐C:F nanoporous films with a low turnon field (1.8V∕μm) are apparently lower than other types of a‐C:F nanostructures. The a‐C:F nanostructures have a greater field-enhancement factor (2500–4000) than other nonaligned multiwall nanotubes. However, the a‐C:F nanostructures follow the Fowler–Nordheim characteristics only in the medium emission current region and they deviate from the characteristics in the low and high emission current regions.

Metal-metal bonding and structures of metal string complexes Cr3(dpa)4Cl2, Cr3(dpa)4(NCS)2, and [Cr3(dpa)4Cl2](PF6) from IR, Raman, and surface-enhanced Raman spectra.

We recorded infrared, Raman, and surface-enhanced Raman scattering (SERS) spectra of metal-string complexes Cr(3)(dpa)(4)X(2) (dpa = di(2-pyridyl)amido, X = Cl, NCS) and [Cr(3)(dpa)(4)Cl(2)](PF(6)) and dipyridylamine (Hdpa) to determine their vibrational frequencies and to study their structures. For the SERS measurements these complexes were adsorbed on silver nanoparticles in aqueous solution to eliminate the constraints of a crystal lattice. From the results of analysis of the vibrational normal modes we assign the infrared band at 346 cm(-1) to the Cr(3) asymmetric stretching vibration of the symmetric form and the Raman line at 570 cm(-1) to the Cr-Cr stretching mode for the unsymmetric form of Cr(3)(dpa)(4)Cl(2). Complex Cr(3)(dpa)(4)Cl(2) exhibits both symmetric (s-) and unsymmetric (u-) forms in solution but Cr(3)(dpa)(4)(NCS)(2) only the s-form. The structures for both complexes in their ground states have the s-form. The oxidized complex [Cr(3)(dpa)(4)Cl(2)](PF(6)) has only a u-form for which the Cr-Cr stretching mode is assigned to the band at 570 cm(-1). From the variation with temperature from 23 to 60 degrees C of the intensity of this line, we obtained the proportion of the u-form Cr(3)(dpa)(4)Cl(2); the enthalpy change is thus obtained to be DeltaH = 46.2 +/- 3.3 kJ mol(-1) and the entropy change is DeltaS = 138 +/- 10.3 J K(-1) mol(-1) for the reaction u-Cr(3)(dpa)(4)Cl(2) <--> s-Cr(3)(dpa)(4)Cl(2). From the spectral intensities and band frequencies in SERS spectra, Hdpa is expected to adsorb on a silver nanoparticle with the amido nitrogen and pyridyl rings tilted from the silver surface, whereas the trichromium complex with the chromium ion line is orthogonal to the silver surface normal in aqueous silver solution.

The crystalline properties of carbon nitride nanotubes synthesized by electron cyclotron resonance plasma

Abstract Carbon nitride nanotubes (CN-NT) have been synthesized by an electron cyclotron resonance chemical vapor deposition (ECR–CVD) system with a mixture of C 2 H 2 and N 2 as precursors without using any catalyst. The carbon nitride nanotubes were synthesized in an anodic alumina membrane as template in which a packed array of parallel, straight and uniform channels with a diameter of approximately 50-nm and 30-μm thick exists. Samples were analyzed by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Preliminary results showed that the properties of the deposited carbon nitride nanostructures depend on process parameters, such as deposited temperature, ratio of the precursors and microwave power. The aligned nanostructures have been verified by FESEM and HRTEM. The FTIR spectra reveal that some of the carbon atoms may have possibly been substituted by oxygen atom in the carbon nitride nanotubes. From the XPS results, N is either bonded to two C atoms (sp 2 pyridine-like type) or to three (sp 3 urotropine-like type) in the hexagonal sheets. The Raman spectrum showed that carbon nitride nanotubes have a high degree of graphitization.