اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدEffect of Contact Interfaces on Quantum Conductance of Armchair Nanotubes
96
0
0.0
(
0
)
تأليف
S. Krompiewski
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Effect of contact interfaces, between metallic single-wall carbon nanotubes (SWCNT) and external electrodes made also of nanotubes, on the electrical conductance is studied. A tight-binding model with both diagonal and off-diagonal disorder, a recursive Green function technique as well as the Landauer formalism are used. The studies are carried out within the coherent transport regime and are focused on: (i) evolution from conductance quantization to resonant tunneling, (ii) SWCNTs length effects and (iii) magnetoresistance. It is shown that the so-called on-resonance devices, i.e. nanotubes having a conductance peak at the Fermi energy, occur with a period of 3 carbon inter-ring spacings. Additionally, the present approach provides an insight into magnetoresistance dependence of SWCNTs on conditions at the contact interface.
قيم البحث
اقرأ أيضاً
We study the contact resistance and the transfer characteristics of back-gated field effect transistors of mono- and bi-layer graphene. We measure specific contact resistivity of ~7kohm*um2 and ~30kohm*um2 for Ni and Ti, respectively. We show that th
e contact resistance is a significant contributor to the total source-to-drain resistance and it is modulated by the back-gate voltage. We measure transfer characteristics showing double dip feature that we explain as the effect of doping due to charge transfer from the contacts causing minimum density of states for graphene under the contacts and in the channel at different gate voltage.
We have calculated the effects of structural distortions of armchair carbon nanotubes on their electrical transport properties. We found that the bending of the nanotubes decreases their transmission function in certain energy ranges and leads to an
increased electrical resistance. Electronic structure calculations show that these energy ranges contain localized states with significant $sigma$-$pi$ hybridization resulting from the increased curvature produced by bending. Our calculations of the contact resistance show that the large contact resistances observed for SWNTs are likely due to the weak coupling of the NT to the metal in side bonded NT-metal configurations.
We have used post-synthesis separation methods based on density gradient ultracentrifugation and DNA-based ion-exchange chromatography to produce aqueous suspensions strongly enriched in armchair nanotubes for spectroscopic studies. Through resonant
Raman spectroscopy of the radial breathing mode phonons, we provide macroscopic and unambiguous evidence that density gradient ultracentrifugation can enrich armchair nanotubes. Furthermore, using conventional, optical absorption spectroscopy in the near-infrared and visible range, we show that interband absorption in armchair nanotubes is strongly excitonic. Lastly, by examining the G-band mode in Raman spectra, we determine that observation of the broad, lower frequency (G^{-}) feature is a result of resonance with non-armchair metallic nanotubes. These findings regarding the fundamental optical absorption and scattering processes in metallic carbon nanotubes lay the foundation for further spectroscopic studies to probe many-body physical phenomena in one dimension.
We investigate the effects of impurity scattering on the conductance of metallic carbon nanotubes as a function of the relative separation of the impurities. First we compute the conductance of a clean (6,6) tube, and the effect of model gold contact
s on this conductance. Then, we compute the effect of introducing a single, two, and three oxygen atom impurities. We find that the conductance of a single-oxygen-doped (6,6) nanotube decreases by about 30 % with respect to that of the perfect nanotube. The presence of a second doping atom induces strong changes of the conductance which, however, depend very strongly on the relative position of the two oxygen atoms. We observe regular oscillations of the conductance that repeat over an O-O distance that corresponds to an integral number of half Fermi-wavelengths ($mlambda_F/2$). These fluctuations reflect strong electron interference phenomena produced by electron scattering from the oxygen defects whose contribution to the resistance of the tube cannot be obtained by simply summing up their individual contributions.
We have used resonant Raman scattering spectroscopy to fully analyze the relative abundances of different (n,m) species in single-walled carbon nanotube samples that are metallically enriched by density gradient ultracentrifugation. Strikingly, the d
ata clearly show that our density gradient ultracentrifugation process enriches the metallic fractions in armchair and near-armchair species. We observe that armchair carbon nanotubes constitute more than 50% of each (2n + m) family.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
