اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدTemperature dependence of exciton recombination in semiconducting single-wall carbon nanotubes
168
0
0.0
(
0
)
تأليف
S. Berger
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We study the excitonic recombination dynamics in an ensemble of (9,4) semiconducting single-wall carbon nanotubes by high sensitivity time-resolved photo-luminescence experiments. Measurements from cryogenic to room temperature allow us to identify two main contributions to the recombination dynamics. The initial fast decay is temperature independent and is attributed to the presence of small residual bundles that create external non-radiative relaxation channels. The slow component shows a strong temperature dependence and is dominated by non-radiative processes down to 40 K. We propose a quantitative phenomenological modeling of the variations of the integrated photoluminescence intensity over the whole temperature range. We show that the luminescence properties of carbon nanotubes at room temperature are not affected by the dark/bright excitonic state coupling.
قيم البحث
اقرأ أيضاً
Semiconducting single-wall carbon nanotubes are classified into two types by means of orbital angular momentum of valley state, which is useful to study their low energy electronic properties in finite-length. The classification is given by an intege
r $d$, which is the greatest common divisor of two integers $n$ and $m$ specifying the chirality of nanotubes, by analyzing cutting lines. For the case that $d$ is equal to or greater than four, two lowest subbands from two valleys have different angular momenta with respect to the nanotube axis. Reflecting the decoupling of two valleys, discrete energy levels in finite-length nanotubes exhibit nearly fourfold degeneracy and its small lift by the spin-orbit interaction. For the case that $d$ is less than or equal to two, in which two lowest subbands from two valleys have the same angular momentum, discrete levels exhibit lift of fourfold degeneracy reflecting the coupling of two valleys. Especially, two valleys are strongly coupled when the chirality is close to the armchair chirality. An effective one-dimensional lattice model is derived by extracting states with relevant angular momentum, which reveals the valley coupling in the eigenstates. A bulk-edge correspondence, relationship between number of edge states and the winding number calculated in the corresponding bulk system, is analytically shown by using the argument principle, which enables us to estimate the number of edge states from the bulk property. The number of edge states depends not only on the chirality but also on the shape of boundary.
We have used a femtosecond pump-probe impulsive Raman technique to explore the polarization dependence of coherent optical phonons in highly-purified and aligned semiconducting single-wall carbon nanotubes (SWCNTs). Coherent phonon spectra for the ra
dial breathing modes (RBMs) exhibit a different monochromatic frequency between the film and solution samples, indicating the presence of differing exciton excitation processes. By varying the polarization of the incident pump beam on the aligned SWCNT film, we found that the anisotropy of the coherent RBM excitation depends on the laser wavelength, which we consider to be associated with the resonant and off-resonant behavior of RBM excitation.
We present a systematic study on low-frequency current fluctuations of nano-devices consisting of one single semiconducting nanotube, which exhibit significant 1/f-type noise. By examining devices with different switching mechanisms, carrier types (e
lectrons vs. holes), and channel lengths, we show that the 1/f fluctuation level in semiconducting nanotubes is correlated to the total number of transport carriers present in the system. However, the 1/f noise level per carrier is not larger than that of most bulk conventional semiconductors, e.g. Si. The pronounced noise level observed in nanotube devices simply reflects on the small number of carriers involved in transport. These results not only provide the basis to quantify the noise behavior in a one-dimensional transport system, but also suggest a valuable way to characterize low-dimensional nanostructures based on the 1/f fluctuation phenomenon.
We present a simple technique which uses a self-aligned oxide etch to suspend individual single-wall carbon nanotubes between metallic electrodes. This enables one to compare the properties of a particular nanotube before and after suspension, as wel
l as to study transport in suspended tubes. As an example of the utility of the technique, we study quantum dots in suspended tubes, finding that their capacitances are reduced owing to the removal of the dielectric substrate.
The circular dichroism (CD) spectra of single-wall carbon nanotubes are calculated using a dipole approximation. The calculated CD spectra show features that allow us to distinguish between nanotubes with different angles of chirality, and diameters.
These results provide theoretical support for the quantification of chirality and its measurement, using the CD lineshapes of chiral nanotubes. It is expected that this information would be useful to motivate further experimental studies.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
