Property by design is one appealing idea in material synthesis but hard to achieve in practice. A recent successful example is the demonstration of van der Waals (vdW) heterostructures, 1-3 in which atomic layers are stacked on each other and different ingredients can be combined beyond symmetry and lattice matching. This concept, usually described as a nanoscale Lego blocks, allows to build sophisticated structures layer by layer. However, this concept has been so far limited in two dimensional (2D) materials. Here we show a class of new material where different layers are coaxially (instead of planarly) stacked. As the structure is in one dimensional (1D) form, we name it "1D vdW heterostructures". We demonstrate a 5 nm diameter nanotube consisting of three different materials: an inner conductive carbon nanotube (CNT), a middle insulating hexagonal boron nitride nanotube

Liquid crystals are mostly formed by self-assembly of organic molecules. In contrast, inorganic materials available as liquid crystals are limited. Here we report the development of liquid-crystalline (LC) hydroxyapatite (HAp), which is an environmentally friendly and biocompatible biomineral. Its alignment behavior, magneto-optical properties, and atomic-scale structures are described. We successfully induce LC properties into aqueous colloidal dispersions of rod-shaped HAp by controlling the morphology of the material using acidic macromolecules. These LC HAp nanorod materials are macroscopically oriented in response to external magnetic fields and mechanical forces. We achieve magnetic modulation of the optical transmission by dynamic control of the LC order. Atomic-scale observations using transmission electron microscopy show the self-organized inorganic/organic hybrid structures of mesogenic nanorods. HAp liquid crystals have potential as bio-friendly functional materials because of their facile preparation, the bio-friendliness of HAp, and the stimuliresponsive properties of these colloidal ordered fluids.

Using low-pressure chemical vapor deposition (LPCVD), we, for the first time, realize the self-limiting growth behavior of monolayer graphene on commercially available electroplated copper foils from a carbon precursor other than methane, and systematically investigate the growth of graphene from ethanol and compare its self-limiting behavior over copper facets with different identities. Results show that the growth of graphene from ethanol in the LPCVD process is a substratemediated process, in which the domains of graphene are determined by the lattice axes on the copper facets. Moreover, during the evolution of the domains, low-index copper facets of Cu(111) and Cu(100) play a critical role in the following self-limiting process of a continuous graphene sheet, whereas the Cu(110) and high-index facets favor nucleation and formation of secondary layers. In addition, a high degree of similarity exists between graphene grown from ethanol and methane, showing that, when the carbon flux is sufficiently low, the self-limiting growth of graphene on copper surfaces using LPCVD is independent of the precursor structure of ethanol and methane.

Grain boundary segregation is a critical issue in materials science because it determines the properties of individual grain boundaries and thus governs the macroscopic properties of materials. Recent progress in electron microscopy has greatly improved our understanding of grain boundary segregation phenomena down to atomistic dimensions, but solute segregation is still extremely challenging to experimentally identify at the atomic scale. Here, we report direct observations of atomic-scale yttrium solute segregation behaviours in an yttria-stabilized-zirconia grain boundary using atomic-resolution energy-dispersive X-ray spectroscopy analysis. We found that yttrium solute atoms preferentially segregate to specific atomic sites at the core of the grain boundary, forming a unique chemically-ordered structure across the grain boundary.

Synthesis of single-walled carbon nanotubes (SWNTs) with well-defined atomic arrangements has been widely recognized in the past few decades as the biggest challenge in the SWNT community, and has become a bottleneck for the application of SWNTs in nano-electronics. Here, we report a selective synthesis of (12, 6) SWNTs with an enrichment of 50%-70% by chemical vapor deposition (CVD) using sputtered Co-W as a catalyst. This is achieved under much milder reduction and growth conditions than those in the previous report using transition-metal molecule clusters as catalyst precursors (Nature, 2014, 510, 522). Meanwhile, in-plane transmission electron microscopy unambiguously identified an intermediate structure of Co6W6C, which is strongly associated with selective growth. However, most of the W atoms disappear after a 5 min CVD growth, which implies that anchoring W may be important in this puzzling Co-W system.

For the intercalation type cathode in lithium-ion batteries, the structural framework of electrode is expected to remain unchanged during lithium insertion and extraction. Unfavorable phase transition in electrode materials, which has been frequently observed, modifies the structural framework, which leads to capacity loss and voltage decay. Here, we track atoms motion/shift in lithium manganese oxide during a phase transition from spinel to rocksalt by using atomically resolved aberration corrected scanning transmission electron microscopy and spectroscopy. We find that when given energy, the transition metal cation can readily hop between oxygen tetrahedral and octahedral sites in oxygen deficient lithium manganese oxide similar to lithium diffusion behavior, which leaves the anion structure framework almost unchanged. During this phase transition, the intermediate state, migration length, and atomic structure of phase boundaries are revealed, and the mechanism is discussed. Our observations help us to understand the past experimental phenomena and provide useful information to stabilize the structure of electrode materials and thus improve the cycling life of lithium-ion batteries.

We synthesize vertically aligned single-walled carbon nanotubes (VA-SWNTs) with subnanometer diameters on quartz (and SiO2/Si) substrates by alcohol CVD using Cu-anchored Co catalysts. The uniform VA-SWNTs with a nanotube diameter of 1 nm are synthesized at a CVD temperature of 800 °C and have a thickness of several tens of μm. The diameter of SWNTs was reduced to 0.75 nm at 650 °C with the G/D ratio maintained above 24. Scanning transmission electron microscopy energy-dispersive X-ray spectroscopy (EDS-STEM) and high angle annular dark field (HAADF-STEM) imaging of the Co/Cu bimetallic catalyst system showed that Co catalysts were captured and anchored by adjacent Cu nanoparticles, and thus were prevented from coalescing into a larger size, which contributed to the small diameter of SWNTs. The correlation between the catalyst size and the SWNT diameter was experimentally clarified. The subnanometer-diameter and high-quality SWNTs are expected to pave the way to replace silicon for next-generation optoelectronic and photovoltaic devices.

Owing to the broken translational symmetry at dislocations, a strain gradient naturally exists around the dislocation cores and can significantly influence the electrical and mechanical properties. We use aberration corrected scanning transmission electron microscopy to directly measure the flexoelectric polarization (∼28  μC cm^{-2}) at dislocation cores in SrTiO_{3}. The polarization charges can interact with the nonstoichiometric dislocation cores and thus impact the electrical activities. Our findings can help us to understand the properties of dislocations in perovskite, providing new insights into the design of new devices via defect engineering such as bicrystal fabrication and thin film growth.