Enhancing and redirecting carbon nanotube photoluminescence by an optical antenna

We observe the angular radiation pattern of single carbon nanotubes' photoluminescence in the back focal plane of a microscope objective and show that the emitting nanotube can be described by a single in-plane point dipole. The near-field interaction between a nanotube and an optical antenna modifies the radiation pattern that is now dominated by the antenna characteristics. We quantify the antenna induced excitation and radiation enhancement and show that the radiative rate enhancement is connected to a directional redistribution of the emission

Exciton decay dynamics in individual carbon nanotubes at room temperature

We studied the exciton decay dynamics of individual semiconducting single-walled carbon nanotubes at room temperature using time-resolved photoluminescence spectroscopy. The photoluminescence decay from nanotubes of the same (n,m) type follows a single exponential decay function, however, with lifetimes varying between about 1 and 40 ps from nanotube to nanotube. A correlation between broad photoluminescence spectra and short lifetimes was found and explained by defects promoting both nonradiative decay and vibronic dephasing

Principles of carbon nanotube dielectrophoresis

Dielectrophoresis (DEP) describes the motion of suspended objects when exposed to an inhomogeneous electric field. It has been successful as a method for parallel and site-selective assembling of nanotubes from a dispersion into a sophisticated device architecture. Researchers have conducted extensive works to understand the DEP of nanotubes in aqueous ionic surfactant solutions. However, only recently, DEP was applied to polymer-wrapped single-walled carbon nanotubes (SWCNTs) in organic solvents due to the availability of ultra-pure SWCNT content. In this paper, the focus is on the difference between the DEP in aqueous and organic solutions. It starts with an introduction into the DEP of carbon nanotubes (CNT-DEP) to provide a comprehensive, in-depth theoretical background before discussing in detail the experimental procedures and conditions. For academic interests, this work focuses on the CNT-DEP deposition scheme, discusses the importance of the electrical double layer, and employs finite element simulations to optimize CNT-DEP deposition condition with respect to the experimental observation. An important outcome is an understanding of why DEP in organic solvents allows for the deposition and alignment of SWCNTs in low-frequency and even static electric fields, and why the response of semiconducting SWCNTs (s-SWCNTs) is strongly enhanced in non-conducting, weakly polarizable media. Strategies to further improve CNT-DEP for s-SWCNT-relevant applications are given as well. Overall, this work should serve as a practical guideline to select the appropriate setting for effective CNT DEP

a Raman scattering study

The longitudinal optical phonon of metallic nanotubes shifts by 23 cm−1 to lower energies when the nanotubes are deposited from a solution onto a substrate. The linewidth increases by 13 cm−1. The changes are explained in terms of shifts in the Fermi energy that influence the Kohn anomaly in the longitudinal optical phonon branch in metallic nanotubes. Using in situ electrochemical Raman measurements we show that the Fermi energy is 0.16 eV below its intrinsic value in metallic nanotubes in solution. Our results impact the application of Raman spectroscopy to distinguish between metallic and semiconducting tubes by examining the high-energy mode line shape

Vanishing Hysteresis in Carbon Nanotube Transistors Embedded in Boron Nitride/Polytetrafluoroethylene Heterolayers

Carbon nanotube field‐effect transistors fabricated on silicon wafers with thermal oxide often suffer from large gate‐voltage hysteresis, induced by charge trapping sites in oxides, surface hydroxyl groups, and the presence of water molecules. Surface functionalization and passivation, as well as vacuum annealing and reduced operating temperature, have shown to diminish or even eliminate hysteresis. Herein, the fabrication of nearly hysteresis‐free transistors on Si/SiO$_{2}$ by embedding carbon nanotubes and the connecting electrodes in a hexagonal boron nitride (h‐BN) bottom layer and a polytetrafluoroethylene (PTFE) top layer is demonstrated. The conditions at which catalyst‐free synthesis of h‐BN on SiO$_{2}$/Si with borazine is obtained, and the subsequent liquid‐phase deposition of PTFE, are discussed. Device transfer curves are measured before and after PTFE deposition. It is found that the hysteresis is reduced after PTFE deposition, but vanishes only after a waiting period of several days. Simultaneously, the on‐state current increases with time. The results give evidence for the absence of trap states in h‐BN/PTFE heterolayers and a high breakthrough field strength in those wafer‐scalable materials

Influence of Cooperation Work on Management Continuity of Ambulatory Cardiovascular Care: A Cross-Sectional Exploratory Study in Germany

Introduction: A wide range of factors influence coordination and continuity of care. The aim of this study was to explore how management continuity of cardiovascular-related ambulatory care is influenced by the following network characteristics: presence of a case coordinator, network reciprocity, network composition and team climate. Methods: This cross-sectional observational study included three written surveys. The primary outcome management continuity of cardiovascular care was measured with the team/cross-boundary scale in the Nijmegen Continuity Questionnaire. The final analysis comprised a multivariate linear multilevel model with the predictors: presence of a case coordinator, network reciprocity, network composition and team climate. Results: Eighteen general practices with 83 health workers and 340 patients participated. The linear multilevel regression analysis showed a positive influence of team climate on cross-boundary continuity of care (b-coefficient 0.44, 95% confidence interval 0.09–0.78, p = 0.02). No statistically significant influence was measured for the other predictors. Discussion: To improve integrated care, therefore, emphasis should also be placed on promoting the team climate within individual practices. Regarding network characteristics, further research is needed, especially in larger practices. Conclusion: This study showed that team climate had an independent, relevant and statistically significant association with cross-boundary continuity of cardiovascular ambulatory care