We present first-and second-order Raman spectra of boron-doped multiwalled carbon nanotubes. The Raman intensities are analyzed as a function of the nominal boron concentration. The intensities of both the D mode and the high-energy mode in the first-order spectra increase with increasing boron concentration, if normalized with respect to a second-order mode. We interpret this result as an indication that the high-energy mode in carbon nanotubes is defect-induced in a similar way as the D mode. Based on this result, we provide a preliminary quantitative relation between the boron concentration and the Raman intensity ratios.

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Atomic resolution images of multiwalled boron nitride nanotubes have been obtained using scanning tunneling microscopy operating at tunneling currents below 20 pA and biases of approximately −2.5 V. Lattice images acquired with negative sample biases exhibit trigonal symmetry that is interpreted as resulting from nitrogen states. Tunneling spectroscopy confirms band gaps between 4.5 eV and 4.8 eV for tube diameters above 5 nm. Tunneling barrier height measurements made using standard current–distance analysis yields Φ∼6.3±0.7 eV for the boron nitride nanotubes.

Articles you may be interested in Nature, geometry, and binding strength of the ammonia-hydrogen chloride dimer determined from the rotational spectrum of ammonium chloride vapor J. Chem. Phys. 88, 4694 (1988); 10.1063/1.453783The rotational spectrum and molecular properties of a hydrogenbonded complex formed between hydrogen cyanide and hydrogen chloride Ground state rotational spectra of the three isotopomers (CH 2 hO'" H 35 CI, (CH 2 hO'" H 31 CI, and (CH 2 hO'" D 35 CI of a short-lived hydrogen-bonded dimer have been detected in the reactive mixture of oxirane and hydrogen chloride by using a fast-mixing nozzle in conjunction with a Balle-Flygare Fourier-transform microwave spectrometer. Rotational constants, centrifugal distortion constants and Cl-nuclear quadrupole coupling constants were determined for each isotopomer. In particular, all four components Xaa' Xbb' X= and Xac of the coupling tensor were obtained. A detailed analysis of the rotational constants allows the conclusion that the dimer has C s symmetry, with a steeply pyramidal arrangement completed at oxygen by the hydrogen bond with HCI. Diagonalization of the complete Cl-nuclear quadrupole coupling tensor leads to the principal axis components XXX' XYY' and Xzz (where z is the HCI direction in the dimer). The angle of rotation a is the angle between the HCI (z) direction and the a-axis direction in the eqUilibrium conformation of the dimer. It is larger by ~ 10° than the angle r between the 0·· 'CI internuclear line and the principal inertial axis a in each case and implies that the hydrogen bond is bent by 180-0 =~16S from the collinear arrangement O"'H-Cl (0=0). The angle 180-0 and the angle cp=76.2° made by the 0" 'CI internuclear line with the extension of the oxirane local C 2 axis are interpreted in terms of a simple model of the hydrogen bond.

The rotational spectra of two symmetric-top isotopomers of the trimethylphosphinehydrogen chloride dimer have been observed by pulsed-nozzle, Fourier-transform microwave spectroscopy and analysed to give the following ground-state spectroscopic constants : B,/MHz D,/kHz D, , / kHz X(CI)/MHz (CHJ3P. ' .H35CI 1005.0221(1) 0.514(2) 41.509(6) -50.486(7) (CHJ3P. ' .H3'CI 974.5109(2) 0.483(3) 39.500(11) -39.823(13)The CI nuclear quadrupole coupling constant x(%I) is used to establish that the description (CH,),P.. .HCI rather than (CH,),&H.. .CI is more appropriate, although a v t r y small extent of proton transfer cannot be ruled out. The former model is used to obtain r(P. .CI) = 3.6131(2) A andk, = 10.48(7) N m-'. A comparison of K(,~CI