Dimensionality plays a critical role in determining the properties of materials due to, for example, the different ways that electrons interact in three-dimensional, twodimensional (2D), and one-dimensional (1D) structures.1-5 The study of dimensionality has a long history in chemistry and physics, although this has been primarily with the prefix “quasi” added to the description of materials; that is, quasi-1D solids, including square-planar platinum chain and metal trichalcogenide compounds,2,6 and quasi2D layered solids, such as metal dichalcogenides and copper oxide superconductors.3-5,7,8 The anisotropy inherent in quasi-1D and -2D systems is central to the unique properties and phases that these materials exhibit, although the small but finite interactions between 1D chains or 2D layers in bulk materials have made it difficult to address the interesting properties expected for the pure low-dimensional systems. Are pure low-dimensional systems interesting and worth pursuing? We believe that the answer to this question is an unqualified yes from the standpoints of both fundamental science and technology. One needs to look no further than past studies of the 2D electron gas in semiconductor heterostructures, which have produced remarkably rich and often unexpected results,9,10 and electron tunneling through 0D quantum dots, which have led to the concepts of the artificial atom and the creation of single electron transistors.11-15 In these cases, lowdimensional systems were realized by creating discrete 2D and 0D nanostructures. 1D nanostructures, such as nanowires and nanotubes, are expected to be at least as interesting and important as 2D and 0D systems.16,17 1D systems are the smallest dimension structures that can be used for efficient transport of electrons and optical excitations, and are thus expected to be critical to the function and integration of nanoscale devices. However, little is known about the nature of, for example, localization that could preclude transport through 1D systems. In addition, 1D systems should exhibit density of states singularities, can have energetically discrete molecularlike states extending over large linear distances, and may show more exotic phenomena, such as the spin-charge separation predicted for a Luttinger liquid.1,2 There are also many applications where 1D nanostructures could be exploited, including nanoelectronics, superstrong and tough composites, functional nanostructured materials, and novel probe microscopy tips.16-29 To address these fascinating fundamental scientific issues and potential applications requires answers to two questions at the heart of condensed matter chemistry and physics research: (1) How can atoms or other building blocks be rationally assembled into structures with nanometer-sized diameters but much longer lengths? (2) What are the intrinsic properties of these quantum wires and how do these properties depend, for example, on diameter and structure? Below we describe investigations from our laboratory directed toward these two general questions. The organization of this Account is as follows. In section II, we discuss the development of a general approach to the rational synthesis of crystalline nanowires of arbitrary composition. In section III, we outline key challenges to probing the intrinsic properties of 1D systems and illustrate solutions to these challenges with measurements of the atomic structure and electronic properties of carbon nanotubes. Last, we discuss future directions and challenges in section IV.

http://cmliris.harvard.edu/assets/AccChemRes_32_435.pdf

Chemistry and Physics in One Dimension: Synthesis and Properties of Nanowires and Nanotubes

Hexagonal boron nitride (h-BN) is a layered material with a graphite-like structure in which planar networks of BN hexagons are regularly stacked. As the structural analogue of a carbon nanotube (CNT), a BN nanotube (BNNT) was first predicted in 1994; since then, it has become one of the most intriguing non-carbon nanotubes. Compared with metallic or semiconducting CNTs, a BNNT is an electrical insulator with a band gap of ca. 5 eV, basically independent of tube geometry. In addition, BNNTs possess a high chemical stability, excellent mechanical properties, and high thermal conductivity. The same advantages are likely applicable to a graphene analogue-a monatomic layer of a hexagonal BN. Such unique properties make BN nanotubes and nanosheets a promising nanomaterial in a variety of potential fields such as optoelectronic nanodevices, functional composites, hydrogen accumulators, electrically insulating substrates perfectly matching the CNT, and graphene lattices. This review gives an introduction to the rich BN nanotube/nanosheet field, including the latest achievements in the synthesis, structural analyses, and property evaluations, and presents the purpose and significance of this direction in the light of the general nanotube/nanosheet developments.

/pdf/boron-nitride-nanotubes-and-nanosheets-4egjcsg6qj.pdf

Boron Nitride Nanotubes and Nanosheets

The current status of research on boron nitride nanotubes (BNNTs)—carbon nanotube structural analogues—is discussed. Latest achievements in BNNT synthesis, morphology, and atomic structure analysis as well as physical, chemical, and functional property evaluations are reviewed. Similarities and differences between structural parameters and properties of BNNTs in comparison with conventional carbon nanotubes are particularly highlighted. Recent breakthroughs in BNNT filling, doping and functionalization, morphology, and electronic structure engineering are examined. Finally, prospective BNNT applications for fabricating field-effect transistors, gas accumulators, and reinforcing polymer films are presented.

Boron Nitride Nanotubes

Nanomaterials are finding increasing use for biomedical applications such as imaging, diagnostics, and drug delivery. While it is well understood that nanoparticle (NP) physico-chemical properties can dictate biological responses and interactions, it has been difficult to outline a unifying framework to directly link NP properties to expected in vitro and in vivo outcomes. When introduced to complex biological media containing electrolytes, proteins, lipids, etc., nanoparticles (NPs) are subjected to a range of forces which determine their behavior in this environment. One aspect of NP behavior in biological systems that is often understated or overlooked is aggregation. NP aggregation will significantly alter in vitro behavior (dosimetry, NP uptake, cytotoxicity), as well as in vivo fate (pharmacokinetics, toxicity, biodistribution). Thus, understanding the factors driving NP colloidal stability and aggregation is paramount. Furthermore, studying biological interactions with NPs at the nanoscale level requires an interdisciplinary effort with a robust understanding of multiple characterization techniques. This review examines the factors that determine NP colloidal stability, the various efforts to stabilize NP in biological media, the methods to characterize NP colloidal stability in situ, and provides a discussion regarding NP interactions with cells.

/pdf/nanoparticle-colloidal-stability-in-cell-culture-media-and-1ndbwya20h.pdf

Nanoparticle colloidal stability in cell culture media and impact on cellular interactions

Multielement nanotubes comprising multiple phases, with diameters of a few tens of nanometers and lengths up to 50 micrometers, were successfully synthesized by means of reactive laser ablation. The experimentally determined structure consists of a β-phase silicon carbide core, an amorphous silicon oxide intermediate layer, and graphitic outer shells made of boron nitride and carbon layers separated in the radial direction. The structure resembles a coaxial nanocable with a semiconductor-insulator-metal (or semiconductor-insulator-semiconductor) geometry and suggests applications in nanoscale electronic devices that take advantage of this self-organization mechanism for multielement nanotube formation.

https://science.sciencemag.org/content/sci/281/5379/973.full.pdf

Coaxial Nanocable: Silicon Carbide and Silicon Oxide Sheathed with Boron Nitride and Carbon

Metal particle catalysed production of nanoscale BN structures

Native alpha-cyclodextrin (alpha-CD) is found to spontaneously form films at aqueous solution/air interfaces. Shape-response measurements to volume perturbations on drops hanging from a capillary indicate that temperature and sodium dodecyl sulfate (SDS) concentration strongly modify the viscoelastic properties of such films. By using isothermal titration calorimetry (ITC), Brewster angle microscopy (BAM), atomic force microscopy (AFM), and molecular dynamics (MD) simulations, it is shown that the films consist of self-assembled nanotubes whose building blocks are cyclodextrin dimers (alpha-CD2) and alpha-CD2-SDS1 complexes.

Cyclodextrin-based self-assembled nanotubes at the water/air interface.

We present the pressure area isotherms for Langmuir films made of calix[8]arene, the calix[8]arene/C60 complex, and the calix[8]arene/C70 complex, all of them measured at 306.1 K. A Brewster angle microscope was used to observe the phases shown by the π−A isotherms. In these three cases, we found a solid phase and its solid−gas coexistence but no expanded liquid phases. The Langmuir films made of calix[8]arene and the calix[8]arene/C60 complex are very similar. The experimental information is consistent with the assumption that C60 is situated inside the cavity of calix[8]arene. The Langmuir films of calix[8]arene and the calix[8]arene/C70 complex are not very similar; we present a discussion to explain the origin of this difference.

Langmuir Films of Calix[8]arene/Fullerene Complexes

https://www.fisica.unam.mx/grupos/liquids2/papers/13.pdf

High resolution electron microscopy studies in carbon soots

The phase diagrams of Langmuir monolayers of heptadecanoic (C17), nonadecanoic (C19), and heneicosanoic (C21) acids have been determined from pressure-area isotherms, and from direct observations of the monolayers using Brewster angle microscopy In this paper, we describe the observed domains, textures and phase boundaries for all mesophases presented by these fatty acids between 2° and 45 °C The phase diagrams of the three fatty acids can be superposed moving the temperature scale according to the number of carbons in the tail of the fatty acids The L2/Ov phase transition, which is not detected through isotherms, was observed in all the fatty acids under study At low temperatures, CS,L2′, and L2″ phases of C21 were observed, as well as, the transitions among them Also, we observed in C21 a new phase located among the phases L2,L2′, and L2″ This phase was found recently, in the relative same place, in the fatty acid C20 with a tilting azimuth between the nearest-neighbor and the next nearest-neighbo

Salvador Ramos

Papers

Metal particle catalysed production of nanoscale BN structures

Cyclodextrin-based self-assembled nanotubes at the water/air interface.

Langmuir Films of Calix[8]arene/Fullerene Complexes

High resolution electron microscopy studies in carbon soots

Langmuir monolayers of C17, C19, and C21 fatty acids: Textures, phase transitions, and localized oscillations