No abstract

We report a new method for the synthesis of boron nitride nanostructures (nBN) using laser chemical vapor decomposition (LCVD). Borazine was used as precursor and excited with two simultaneous radiations, the fundamental and second YAG laser harmonics. If only one of the two radiations is employed, no reaction takes place. Abundant BN powder is obtained aer one hour of laser radiation. e BN yield obtained with the LCVD technique is about 83% by weight. e BN material was characterized using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. ey all indicate that the BN powder consists of a mixture of hexagonal and cubic BN nanostructures. No other BN phases or stoichiometries were found. e size of the resulting BN nanostructures is in the range of 20-100 nm and their B : N composition is 1 : 1. A simpli�ed mechanism involving laser-excited states followed by photoinduced removal of hydrogen is proposed to understand the synthesis of BN nanopowder by LCVD of borazine.

The room-temperature photosensitivity of sulfur-doped micro-, submicro-, and nano-crystalline diamond films synthesized by hot-filament chemical vapor deposition was studied. The structure and composition of these diamond materials were characterized by Raman spectroscopy, scanning electron microscopy, and x-ray diffraction. The ultraviolet (UV) sensitivity and response time were studied for the three types of diamond materials using a steady-state broad UV excitation source and two pulsed UV laser radiations. It was found that they have high sensitivity in the UV region (as high as 109 s−1 mV−1 range), a linear response in a broad spectral range below 320 nm, photocurrents around ∼10−5 A, and a short response time better than 100 ns, which is independent of fluency intensity. A phenomenological model was applied to help understand the role of defects and dopant concentration on the materials’ photosensitivity.

No abstract

Boron carbonitride nanotubes (BCNNTs) were grown with high yield by arc discharge without catalyst particles or pre-grown template nanostructures. Two types of nanotubes (NTs) were formed: thin NTs with diameters of 10-15 nm and thick NTs with diameters of 25-50 nm, all multiwall. Transmission electron microscopy, electron energy loss spectroscopy, and Raman spectroscopy analyses indicate that the thin NTs are carbon NTs (CNTs) while the thick NTs are BCNNTs wrapped around CNTs. The growth kinetic appears to be faster for CNTs than for BCNNTs. Through the concerted substitution of B and N for C in the in situ grown CNTs, template growth of BCNNTs follows the CNTs growth without causing topological changes.