Positron Spectroscopy Study of Structural Defects and Electronic Properties of Carbon Nanotubes

The advantages and restrictions of different positron spectroscopy methods in the study of electronic properties of multilayer carbon nanotubes (MWCNTs) with metallic and semiconductor types of conductivity are considered. The defects’ influence on the parameters of the MWCNTs’ electronic structure is established via method of the angular correlation of annihilation radiation (ACAR). Analysis of the results shows that annihilation occurs with both σ -electrons (within the interlayer intervals), quasi-free electrons, and electrons of unsaturated covalent bonds. As determined, the increase in the defects’ concentration results to an increase in the radius of localization of the electron wave function ( r m 1 ) within the interlayer inter-vals and to an increase in the quasi-free electron concentration. Due to the formation of edge dislocations in the MWCNTs, the doubling of r m 1 (up to 0.25 nm), the hybridization of unsaturated and stretched σ -bonds, and, as a consequence, the increase of the concentration of conduction electrons occurs. The high sensitivity of the positrons to defects can be used to develop methods of MWCNTs’ attestation and defect identification; the 2 r mb , 2 r mi , and R values obtained from the ACAR spectra are the thickness of the layer, the interlayer distance, and the effective radius of free volume of the MWCNTs, respectively. ñòè. Ìåòîäîì óãëîâîé êîððåëÿöèè àííèãèëÿöèîííîãî èçëó÷åíèÿ (ÓÊÀÈ) óñòàíîâëåíî âëèÿíèå äåôåêòîâ íà ïàðàìåòðû ýëåêòðîííîé ñòðóêòóðû ÌÓÍÒ. Àíàëèç ðåçóëüòàòîâ ïîêàçàë, ÷òî àííèãèëÿöèÿ ïðîèñõîäèò ñ σ -ýëåêòðîíàìè (â ìåæñëîåâûõ ïðîìåæóòêàõ), ñ êâàçèñâîáîäíûìè ýëåêòðîíàìè è ñ ýëåêòðîíàìè íåíàñûùåííûõ êîâàëåíòíûõ ñâÿçåé. Ïîêàçàíî, ÷òî ðîñò êîíöåíòðàöèè äåôåêòîâ ïðèâî-äèò ê óâåëè÷åíèþ ðàäèóñà ëîêàëèçàöèè âîëíîâîé ôóíêöèè ýëåêòðîíîâ ( r m 1 ) â ìåæñëîåâûõ ïðîìåæóòêàõ è ðîñòó äîëè êâàçèñâîáîäíûõ ýëåêòðîíîâ. Âñëåäñòâèå îáðàçîâàíèÿ êðàåâûõ äèñëîêàöèé â ÌÓÍÒ ïðîèñõîäÿò óäâàèâàíèå r m 1 (äî 0,25 íì), ãèáðèäèçàöèÿ íåíàñûùåííûõ è ðàñòÿíóòûõ σ -ñâÿçåé è, êàê ñëåäñòâèå, ðîñò êîíöåíòðàöèè ýëåêòðîíîâ ïðîâîäèìîñòè. Âûñîêàÿ ÷óâñòâèòåëüíîñòü ïîçèòðîíîâ ê äåôåêòàì ìîæåò áûòü èñïîëüçîâàíà äëÿ ðàçðàáîòêè ìåòîäîâ àòòåñòàöèè ÌÓÍÒ è èäåíòèôèêàöèè äåôåêòîâ; âåëè÷èíû 2 r mb , 2 r mi è R , ïîëó÷åííûå èç ñïåêòðîâ