Controlling Nonequilibrium Phonon Populations in Single-Walled Carbon Nanotubes

Abstract

We studied spatially isolated single-walled carbon nanotubes (SWNTs) immobilized in a quasi-planar optical λ/2-microresonator using confocal microscopy and spectroscopy. The modified photonic mode density within the resonator is used to selectively enhance or inhibit different Raman transitions of SWNTs. Experimental spectra are presented that exhibit single Raman bands only. Calculations of the relative change in the Raman scattering cross sections underline the potential of our microresonator for the optical control of nonequilibrium phonon populations in SWNT.The control of the vibrational degrees of freedom or, in other words, the phonon populations in molecular nanostructures like single-walled carbon nanotubes (SWNT) is one of the major goals in nanoscience. 1,2 The electronic structure of SWNTs, see, e.g., refs 3 and 4, is highly susceptible to electron-phonon interactions, and nonequilibrium phonon populations can drastically alter device properties. Hot phonon electron scattering, for example, is known to saturate the charge transport along SWNTs.5-14 As a result, the application of SWNTs in electronic and optoelectronic devices, e.g., 15 could be limited. In the following, we demonstrate the potential of a planar microresonator for the optical control of nonequilibrium phonon populations in SWNTs, i.e., phonon populations that are driven out of thermal equilibrium as imposed by the modified photonic mode density in the presence of the microresonator. Moreover, we describe a strategy for controlling hot phonons in electrically driven SWNTs.The efficiency of spontaneous radiative transitions in optical λ/2 microresonators, i.e., resonators with mirror spacings L of one-half emission wavelength λ of embedded emitters, is determined by the local photonic mode density F cav (L) that can be enhanced and inhibited with respect to the corresponding value F 0 in free (nonconfined) space; see, e.g., ref 16 and references therein. Accordingly, both luminescence and Raman scattering processes of embedded emitters can be controlled by enhancement and inhibition of the spontaneous emission rate Γ cav 17,18 or the Raman scattering cross section σ cav , 19,20 respectively, since both scale with the photonic mode density following 21 In Raman scattering processes the radiative transition is accompanied by the creation (destruction) of a phonon. Hence, it should be possible to populate (depopulate) a specific phonon mode in an embedded SWNT using microresonator-controlled Stokes (anti-Stokes) Raman scattering.In Figure 1a, a schematic of the microresonator is shown. The sample was prepared from a poly(methyl methacrylate) (PMMA)/dichloroethane solution containing purified SWNT with a diameter distribution ranging from 0.8 to 1.8 nm (BuckyUSA). A droplet of the solution was enclosed between two silver mirrors. After evaporation of the dichloroethane, the PMMA film fixed the two mirrors and exhibited immobilized SWNT structures spatially separated in the order of 1 µm. Light passing the microresonator in the λ /2-...

Degradation and Failure of Field Emitting Carbon Nanotube Arrays

“…8 Based on the simulations performed, the stress in the CNTs at various applied bias fields and varying diameters were estimated using Eq. (5). The results are shown in Figure 6.…”

“…1 2 However, in a patterned array of CNT field emitters one observes fluctuation of collective field emission current, often with large spikes, and failure of CNTs. 3 4 Several studies have been reported, which shed light on various different possible mechanisms such as electrodynamic force activated failure in isolated CNT, 4 electron-phonon interaction effect causing degradation in emission current, 5 electrical breakdown 6 7 and thermal degradation of isolated CNTs. [8][9][10] Such degradation mechanisms have their origin in (i) the electro-mechanical force field leading to the deformation of CNTs and (ii) coupled electronphonon transport, thereby, producing temperature spikes under high electric field, and (iii) thermo-mechanically activated fracture of the tubular grapehene sheet.…”

Power dependence of Klyshko's Stokes-anti-Stokes correlation in the inelastic scattering of light

“…In reciprocal space, the logarithmically diverging two-dimensional Van-Hove singularity at the hexagonal saddle (M) point [16] strongly enhances the generation and recombination of electron-hole pairs at the aS photon energy [10,17]. The SaS event is also expected to play a role in other low dimensional materials [18], where phase-space reduction becomes important.…”

Cavity-controlled, electrically-induced infrared emission from a single single-wall carbon nanotube (SWCT)

“…Cavity-controlled infrared emission originating from radiative electron-hole recombination in an individual SWCT is experimentally observed complementing studies of optically excited Raman scattering of cavity-confined SWCTs [6]. The resulting emission spectrum is narrowed by a factor of 7 with respect to the emission spectrum measured from the same SWCT in free (non-confined) space and is essentially determined by the quality (Q) factor of the photonic cavity.…”