Modeling the Growth of Single-Wall Carbon Nanotubes

Monitoring the Formation of Fibrin Clots as Part of the Coagulation Cascade Using Fluorescent Single-Walled Carbon Nanotubes

Blood coagulation is a critical defense mechanism against bleeding that results in the conversion of liquid blood into a solid clot through a complicated cascade, which involves multiple clotting factors. One of the final steps in the coagulation pathway is the conversion of fibrinogen to insoluble fibrin mediated by thrombin. Because coagulation disorders can be life-threatening, the development of novel methods for monitoring the coagulation cascade dynamics is of high importance. Here, we use near-infrared (NIR)-fluorescent single-walled carbon nanotubes (SWCNTs) to image and monitor fibrin clotting in real time. Following the binding of fibrinogen to a tailored SWCNT platform, thrombin transforms the fibrinogen into fibrin monomers, which start to polymerize. The SWCNTs are incorporated within the clot and can be clearly visualized in the NIR-fluorescent channel, where the signal-to-noise ratio is improved compared to bright-field imaging in the visible range. Moreover, the diffusion of individual SWCNTs within the fibrin clot gradually slows down after the addition of thrombin, manifesting a coagulation rate that depends on both fibrinogen and thrombin concentrations. Our platform can open new opportunities for coagulation disorder diagnostics and allow for real-time monitoring of the coagulation cascade with a NIR optical signal output in the biological transparency window.

Melting properties of AgxPt1-x nanoparticles

At the nanoscale, materials exhibit unique properties that differ greatly from those of the bulk state. In the case of Ag_xPt_1-x nanoalloys, we aimed to study the solid-liquid transition of nanoparticles of different sizes and compositions. This system is particularly interesting since Pt has a high melting point (2041 K compared to 1035 K for Ag) which could keep the nanoparticle solid during different catalytic reactions at relatively high temperatures, such as we need in the growth of nanotubes. We performed atomic scale simulations using a semi-empirical potential implemented in a Monte Carlo code at constant temperature and chemical composition in a canonical ensemble. We observed that the melting temperature decreases with decreasing size (pure systems and alloys) and increasing Ag content. We show that the melting systematically passes through an intermediate stage with a crystalline core (pure platinum or mixed PtAg depending on the composition) and a pure silver liquid skin, which strongly questions the idea of having a faceted solid particle in catalytic reactions for carbon nanotube synthesis.

Growth modes of single-walled carbon nanotubes on catalysts

Understanding the growth mechanism of single-walled carbon nanotubes (SWCNTs) and achieving selective growth requires insights into the catalyst structure-function relationship. Using an in situ aberration-corrected environmental transmission electron microscope, we reveal the effects of the state and structure of catalysts on the growth modes of SWCNTs. SWCNTs grown from molten catalysts via a vapor-liquid-solid process generally present similar diameters to those of the catalysts, indicating a size correlation between nanotubes and catalysts. However, SWCNTs grown from solid catalysts via a vapor-solid-solid process always have smaller diameters than the catalysts, namely, an independent relationship between their sizes. The diameter distribution of SWCNTs grown from crystalline Co₇W₆, which has a unique atomic arrangement, is discrete. In contrast, nanotubes obtained from crystalline Co are randomly dispersed. The different growth modes are linked to the distinct chiral selectivity of SWCNTs grown on intermetallic and monometallic catalysts. These findings will enable rational design of catalysts for chirality-controlled SWCNTs growth.

Why Carbon Nanotubes Grow

Despite three decades of intense research efforts, the most fundamental question "why do carbon nanotubes grow?" remains unanswered. In fact, carbon nanotubes (CNTs) should not grow since the encapsulation of a catalyst with graphitic carbon is energetically more favorable than CNT growth in every aspect. Here, we answer this question using a theoretical model based on extensive first-principles and molecular dynamics calculations. We reveal a historically overlooked yet fundamental aspect of the CNT-catalyst interface, viz., that the interfacial energy of the CNT-catalyst edge is contact angle-dependent. The contact angle increases via graphitic cap lift-off, drastically decreasing the interfacial formation energy by up to 6-9 eV/nm, overcoming van der Waals cap-catalyst adhesion, and driving CNT growth. Mapping this remarkable and simple interplay allows us to understand, for the first time, why CNTs grow.

Chirality Pure Carbon Nanotubes: Growth, Sorting, and Characterization

Single-walled carbon nanotubes (SWCNTs) have been attracting tremendous attention owing to their structure (chirality) dependent outstanding properties, which endow them with great potential in a wide range of applications. The preparation of chirality-pure SWCNTs is not only a great scientific challenge but also a crucial requirement for many high-end applications. As such, research activities in this area over the last two decades have been very extensive. In this review, we summarize recent achievements and accumulated knowledge thus far and discuss future developments and remaining challenges from three aspects: controlled growth, postsynthesis sorting, and characterization techniques. In the growth part, we focus on the mechanism of chirality-controlled growth and catalyst design. In the sorting part, we organize and analyze existing literature based on sorting targets rather than methods. Since chirality assignment and quantification is essential in the study of selective preparation, we also include in the last part a comprehensive description and discussion of characterization techniques for SWCNTs. It is our view that even though progress made in this area is impressive, more efforts are still needed to develop both methodologies for preparing ultrapure (e.g., >99.99%) SWCNTs in large quantity and nondestructive fast characterization techniques with high spatial resolution for various nanotube samples.

Hybrid Organic/Inorganic Nano-I-Beam for Structural Nano-mechanics

For years Carbon nano-tube has shown merits in industrial applications including high structural strength-to-weight ratio. However, from structural mechanics perspective the tube geometrical cross-section is less favored for providing high structural stiffness and strength. Hybrid Organic/Inorganic Nano-I-Beam is thus introduced for improved Structural Nano-mechanics. It has been found that both Wide Flange Nano-I-Beam and Equal Flange & Web Nano-I-beam provide higher structural stiffness and less induced stress and thus longer service life than Nano-Tube. It has been also found that Wide Flange Nano-I-Beam provides higher structural stiffness and less induced stress and thus longer service life than Equal Flange & Web Nano-I-beam. A thermodynamic model of the growth of nano-tubes accounting for vibrational entropy is presented. The results have cost-effectively potential benefit in applications such as nano-heat engines & sensors.

Tuning bimetallic catalysts for a selective growth of SWCNTs

Recent advances in structural control during the synthesis of SWCNTs have in common the use of bimetallic nanoparticles as catalysts, despite the fact that their exact role is not fully understood. We therefore analyze the effect of the catalyst's chemical composition on the structure of the resulting SWCNTs by comparing three bimetallic catalysts (FeRu, CoRu and NiRu). A specific synthesis protocol is designed to impede the catalyst nanoparticle coalescence mechanisms and stabilize their diameter distributions throughout the growth. Owing to the ruthenium component which has a limited carbon solubility, tubes grow in tangential mode and their diameter is close to that of their seeding nanoparticles. By using the as-synthesized SWCNTs as a channel material infield effect transistors, we show how the chemical composition of the catalysts and temperature can be used as parameters to tune the diameter distribution and semiconducting-to-metallic ratio of SWCNT samples. Finally, a phenomenological model, based on the dependence of the carbon solubility as a function of catalyst nanoparticle size and nature of the alloying elements, is proposed to interpret the results.

Carbon Nanotubes and Related Nanomaterials: Critical Advances and Challenges for Synthesis toward Mainstream Commercial Applications

Advances in the synthesis and scalable manufacturing of single-walled carbon nanotubes (SWCNTs) remain critical to realizing many important commercial applications. Here we review recent breakthroughs in the synthesis of SWCNTs and highlight key ongoing research areas and challenges. A few key applications that capitalize on the properties of SWCNTs are also reviewed with respect to the recent synthesis breakthroughs and ways in which synthesis science can enable advances in these applications. While the primary focus of this review is on the science framework of SWCNT growth, we draw connections to mechanisms underlying the synthesis of other 1D and 2D materials such as boron nitride nanotubes and graphene.