Properties of one-dimensional molybdenum nanowires in a confined environment

A Universal Method to Transform Aromatic Hydrocarbon Molecules into Confined Carbyne inside Single-Walled Carbon Nanotubes

Carbyne, a sp1-hybridized allotrope of carbon, is a linear carbon chain with exceptional theoretically predicted properties that surpass those of sp2-hybridized graphene and carbon nanotubes (CNTs). However, the existence of carbyne has been debated due to its instability caused by Peierls distortion, which limits its practical development. The only successful synthesis of carbyne has been achieved inside CNTs, resulting in a form known as confined carbyne (CC). However, CC can only be synthesized inside multiwalled CNTs, limiting its property-tuning capabilities to the inner tubes of the CNTs. Here, we present a universal method for synthesizing CC inside single-walled CNTs (SWCNTs) with diameters of 0.9-1.3 nm. Aromatic hydrocarbon molecules are filled inside SWCNTs and subsequently transformed into CC under low-temperature annealing. A variety of aromatic hydrocarbon molecules are confirmed as effective precursors for the formation of CC, with Raman frequencies centered around 1861 cm-1. Enriched (6,5) and (7,6) SWCNTs with diameters less than 0.8 nm are less effective than the SWCNTs with diameters of 0.9-1.3 nm for CC formation. Furthermore, resonance Raman spectroscopy reveals that the optical band gap of the CC at 1861 cm-1 is 2.353 eV, which is consistent with the result obtained using a linear relationship between the Raman frequency and optical band gap. This approach provides a versatile route for synthesizing CC from various precursor molecules inside diverse templates, which is not limited to SWCNTs but could extend to any templates with appropriate size, including molecular sieves, zeolites, boron nitride nanotubes, and metal-organic frameworks.

One-Dimensional van der Waals Heterostructures: A Perspective

As a new frontier in low-dimensional material research, van der Waals (vdW) heterostructures, represented by 2D heterostructures, have attracted tremendous attention due to their unique properties and potential applications. The emerging 1D heterostructures open new possibilities for the field with expectant unconventional properties and yet more challenging preparation pathways. This Perspective aims to give an overall understanding of the state-of-the-art growth strategies and fantastic properties of the 1D heterostructures and provide an outlook for further development based on the controlled preparation, which will bring up a variety of applications in high-performance electronic, optoelectronic, magnetic, and energy storage devices. A quick rise of the fundamentals and application study of 1D heterostructures is anticipated.

Applications of Filled Single-Walled Carbon Nanotubes: Progress, Challenges, and Perspectives

Single-walled carbon nanotubes (SWCNTs), which possess electrical and thermal conductivity, mechanical strength, and flexibility, and are ultra-light weight, are an outstanding material for applications in nanoelectronics, photovoltaics, thermoelectric power generation, light emission, electrochemical energy storage, catalysis, sensors, spintronics, magnetic recording, and biomedicine. Applications of SWCNTs require nanotube samples with precisely controlled and customized electronic properties. The filling of SWCNTs is a promising approach in the fine-tuning of their electronic properties because a large variety of substances with appropriate physical and chemical properties can be introduced inside SWCNTs. The encapsulation of electron donor or acceptor substances inside SWCNTs opens the way for the Fermi-level engineering of SWCNTs for specific applications. This paper reviews the recent progress in applications of filled SWCNTs and highlights challenges that exist in the field.

Metal Cluster Size-Dependent Activation Energies of Growth of Single-Chirality Single-Walled Carbon Nanotubes inside Metallocene-Filled Single-Walled Carbon Nanotubes

By combining in situ annealing and Raman spectroscopy measurements, the growth dynamics of nine individual-chirality inner tubes (8,8), (12,3), (13,1), (9,6), (10,4), (11,2), (11,1), (9,3) and (9,2) with diameters from ~0.8 to 1.1 nm are monitored using a time resolution of several minutes. The growth mechanism of inner tubes implies two successive stages of the growth on the carburized and purely metallic catalytic particles, respectively, which are formed as a result of the thermally induced decomposition of metallocenes inside the outer SWCNTs. The activation energies of the growth on carburized Ni and Co catalytic particles amount to 1.85–2.57 eV and 1.80–2.71 eV, respectively. They decrease monotonically as the tube diameter decreases, independent of the metal type. The activation energies of the growth on purely metallic Ni and Co particles equal 1.49–1.91 eV and 0.77–1.79 eV, respectively. They increase as the tube diameter decreases. The activation energies of the growth of large-diameter tubes (d_t = ~0.95–1.10 nm) on Ni catalyst are significantly larger than on Co catalyst, whereas the values of small-diameter tubes (d_t = ~0.80–0.95 nm) are similar. For both metals, no dependence of the activation energies on the chirality of inner tubes is observed.

Crystallization in Confinement

Many crystallization processes of great importance, including frost heave, biomineralization, the synthesis of nanomaterials, and scale formation, occur in small volumes rather than bulk solution. Here, the influence of confinement on crystallization processes is described, drawing together information from fields as diverse as bioinspired mineralization, templating, pharmaceuticals, colloidal crystallization, and geochemistry. Experiments are principally conducted within confining systems that offer well-defined environments, varying from droplets in microfluidic devices, to cylindrical pores in filtration membranes, to nanoporous glasses and carbon nanotubes. Dramatic effects are observed, including a stabilization of metastable polymorphs, a depression of freezing points, and the formation of crystals with preferred orientations, modified morphologies, and even structures not seen in bulk. Confinement is also shown to influence crystallization processes over length scales ranging from the atomic to hundreds of micrometers, and to originate from a wide range of mechanisms. The development of an enhanced understanding of the influence of confinement on crystal nucleation and growth will not only provide superior insight into crystallization processes in many real-world environments, but will also enable this phenomenon to be used to control crystallization in applications including nanomaterial synthesis, heavy metal remediation, and the prevention of weathering.

Constraint spaces in carbon materials

Nano-sized pores in carbon materials are recently known to give certain constraints to the encapsulated materials by keeping them inside, accompanied with some changes in their structure, morphology, stability, etc. Consequently, nano-sized pores endow the constrained materials with improved performances in comparison with those prepared by conventional processes. These pores may be called "constraint spaces" in carbon materials. Here, we review the experimental results related to these constraint spaces by classifying as nanochannels in carbon nanotubes, nanopores and nanochannels in various porous carbons, and the spaces created by carbon coating.

Extraction of Linear Carbon Chains Unravels the Role of the Carbon Nanotube Host

Linear carbon chains (LCCs) have been shown to grow inside double-walled carbon nanotubes (DWCNTs), but isolating them from this hosting material represents one of the most challenging tasks toward applications. Herein we report the extraction and separation of LCCs inside single-walled carbon nanotubes (LCCs@SWCNTs) extracted from a double-walled host LCCs@DWCNTs by applying a combined tip-ultrasonic and density gradient ultracentrifugation (DGU) process. High-resolution transmission electron microscopy, optical absorption, and Raman spectroscopy show that not only short LCCs but clearly long LCCs (LLCCs) can be extracted and separated from the host. Moreover, the LLCCs can even be condensed by DGU. The Raman spectral frequency of LCCs remains almost unchanged regardless of the presence of the outer tube of the DWCNTs. This suggests that the major importance of the outer tubes is making the whole synthesis viable. We have also been able to observe the interaction between the LCCs and the inner tubes of DWCNTs, playing a major role in modifying the optical properties of LCCs. Our extraction method suggests the possibility toward the complete isolation of LCCs from CNTs.

Facile and novel synthetic method to prepare nano molybdenum and its catalytic activity

This study reports on a facile and economical synthetic method to prepare nano molybdenum by solid-state reaction technique. Metallic nano molybdenum was synthesised from molybdenum trioxide, molybdenum IV oxide and molybdenum VI oxide through thermal decomposition technique. Metallic nano molybdenum prepared from molybdenum IV oxide was used to study the catalytic effect of molybdenum nanoparticles on the growth of Anabaena sp. The increase in concentration of nano molybdenum from 0.1 to 100% in BG11 (N⁻ Mo⁻ + nano Mo) medium increases heterocyst frequency. The chlorophyll and protein content in Anabaena sp. was found to improve when compared with bulk molybdenum particles and showed a positive influence to be used as a nano nutrient for Anabaena sp.

Mechanical properties and thermal stability of ultrathin molybdenum nanowires

The most stable structures of three ultrathin molybdenum (Mo) nanowires were predicted by the simulated annealing basin-hopping method (SABH) with the penalty algorithm.

Copper@polypyrrole nanocables

A simple hydrothermal redox reaction between microcrystalline CuOHCl and pyrrole leads to the isolation of striking nanostructures formed by polypyrrole-coated copper nanocables. These multicomponent cables that feature single-crystalline face-centered cubic Cu cores (ca. 300 nm wide and up to 200 μm long) are smoothly coated by conducting polypyrrole, which in addition to its functionality, offers protection against oxidation of the metal core.

Structure and electronic properties of molybdenum monatomic wires encapsulated in carbon nanotubes

Monatomic chains of molybdenum encapsulated in single-walled carbon nanotubes (CNTs) of different chiralities are investigated using density functional theory. We determine the optimal size of the CNT for encapsulating a single atomic wire, as well as the most stable atomic arrangement adopted by the wire. We also study the transport properties in the ballistic regime by computing the transmission coefficients and tracing them back to the electronic conduction channels of the wire and the host. We predict that CNTs of appropriate radii encapsulating a Mo wire have metallic behavior, even if both the nanotube and the wire are insulators. Therefore, encapsulation of Mo wires in CNTs is a way to create conductive quasi-one-dimensional hybrid nanostructures.

Coaxial metal nano-/microcables with isolating sheath: synthetic methodology and their application as interconnects

Synthesis of coaxial nano-/microcables has been an intensive research subject due to their heterogeneous structures, tuneable properties, and important applications in nano-/micrometer-scale electronic and optoelectronic devices. Research on the fabrication of nanocables via solution strategies has made great progress in the past few years. In this Research News article, rapidly emerging new solution strategies such as hydrothermal carbonization (HTC) and synergistic soft-hard templates (SSHTs) are highlighted. Unique and flexible coaxial nano-/microcables synthesized by those methods have obvious advantages such as long-term stability and their electrical transport properties, compared with bare counterparts, suggesting that they are potential candidates as interconnects in the future.

Interaction of small gold clusters with carbon nanotube bundles: formation of gold atomic chains

We use first-principles density functional theory to simulate the interaction of bundles of semiconducting (10, 0) and metallic (6, 6) carbon nanotubes (CNTs) with small gold clusters (Au(n), n = 3, 5) inserted in their interstitial spaces. We find that gold clusters spontaneously evolve to form atomic chains along the axis of nanotubes and induce weak metallicity in the semiconducting nanotubes through charge transfer. We further show that a similar structural evolution of Pt(3) clusters occurs in the interstitial spaces of a (10, 0) CNT bundle. Our calculations show that these structural changes, along with interesting changes in the electronic structure, occur at moderate pressures that are readily achievable in a laboratory, and should be relevant to devices that make use of gold-nanotube contacts.

Interactions between metals and carbon nanotubes: at the interface between old and new materials

The article reviews the interaction between crystalline metals and carbon nanotubes in nanocomposite systems. Starting with an introduction to the chemical interaction between metal atoms and graphitic layers, an overview of the fields of nanotechnology is given where metal-carbon interaction comes into play. The interface between metals and carbon nanotubes is of interest in junctions between nanotubes and their periphery, for example in metallic contacts for electronic devices or in metal supports for carbon nanotube components. Furthermore, metals determine the catalytic growth of carbon nanotubes. The behaviour of individual metal atoms in or on carbon nanotubes is treated as well as the interaction between crystalline metals and nanotube surfaces. Emphasis is put on the common mechanisms of metal-carbon interaction that play a role in such different fields as the electrical transport through a metal-nanotube contact or the catalytic growth of nanotubes from metal particles.