We report total-energy electronic structure calculations that provide energetics of encapsulation of C60 in the carbon nanotube and electronic structures of the resulting carbon peapods. We find that the encapsulating process is exothermic for the (10,10) nanotube, whereas the processes are endothermic for the (8,8) and (9,9) nanotubes, indicative that the minimum radius of the nanotube for the encapsulation is 6.4 A. We also find that the C(60)@(10,10) is a metal with multicarriers each of which distributes either along the nanotube or on the C60 chain. This unusual feature is due to the nearly free electron state that is inherent to hierarchical solids with sufficient space inside.

Okada, Saito, and Oshiyama Reply: As we mentioned [1], there are only three polymerized C 60 phases which have been synthesized under pressure and whose atomic structure has been identified to date; one-dimensional orthorhombic, two-dimensional tetragonal, and twodimensional rhombohedral phases [2]. Although there have been a lot of experimental studies to explore new phases of carbon using pressure synthesis from solid C 60 [3][4][5][6] as Brazhkin and Lyapin commented [7], in most cases it is not clear what type of atomic structure the synthesized material has: Sometimes amorphous, sometimes crystal, sometimes a mixture of diamond and graphite, and sometimes totally unidentified at all.Some materials obtained via pressure synthesis from solid C 60 were reported to be superhard or even "ultrahard" (harder than diamond) and were inferred to be three-dimensional (3D) C 60 polymers from their broad x-ray diffraction profiles [8,9]. For these "superhard 3D C 60 polymers," atomic-scale network topologies had not been reported so far. Only quite recently, candidates for the atomic coordinates have been proposed [10] for the first time.In our Letter [1] we tried to provide a firm theoretical framework to consider synthesis and properties of 3D C 60 polymers. Starting from the tetragonal phase of 2D C 60 polymer, we found an ordered 3D C 60 polymer which had not been identified before and exhibited fascinating properties as described in the Letter. From the point of synthesis, for instance, the radial distribution function which experimentalists sometimes rely on to determine the structure is found to not be a simple reflection of the microscopic structures. Also the system is expected to be a candidate for a new elemental superconductor consisting entirely of carbon. At the same time, we found that our system was not a superhard or ultrahard material. Its bulk modulus is found to be 1 order of magnitude smaller than diamond [1].The present theoretical treatment (density-functional pseudopotential procedure) is expected to have enough accuracy to discuss relative hardness of various carbon based materials [11,12]. Hence there is no doubt that the system we found does not correspond directly to so-called superhard 3D C 60 polymers. On the other hand, generally it is useful to compare theoretical and experimental results carefully to innovate new materials. It is especially important in the field of nanostructure materials consisting of carbon and/or other covalent-bond elements. Their physical properties are known to depend strongly on the network topology of covalent bonds as has been clearly demonstrated in the case of carbon nanotubes [13,14].Sometimes the target new materials, with novel properties to be synthesized, can be given from the theoretical study. In this respect, a comparison between theory and experiment done by Brazhkin and Lyapin [7] is worth further consideration. The possibility of the presence of various different phases in pressure-polymerized 3D C 60 is an interesting issue to be studied theoreti...

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

In the pursuit of ultrasmall electronic components, monolayer electronic devices have recently been fabricated using transition-metal dichalcogenides. Monolayers of these materials are semiconducting, but nanowires with stoichiometry MX (M = Mo or W, X = S or Se) have been predicted to be metallic. Such nanowires have been chemically synthesized. However, the controlled connection of individual nanowires to monolayers, an important step in creating a two-dimensional integrated circuit, has so far remained elusive. In this work, by steering a focused electron beam, we directly fabricate MX nanowires that are less than a nanometre in width and Y junctions that connect designated points within a transition-metal dichalcogenide monolayer. In situ electrical measurements demonstrate that these nanowires are metallic, so they may serve as interconnects in future flexible nanocircuits fabricated entirely from the same monolayer. Sequential atom-resolved Z-contrast images reveal that the nanowires rotate and flex continuously under momentum transfer from the electron beam, while maintaining their structural integrity. They therefore exhibit self-adaptive connections to the monolayer from which they are sculpted. We find that the nanowires remain conductive while undergoing severe mechanical deformations, thus showing promise for mechanically robust flexible electronics. Density functional theory calculations further confirm the metallicity of the nanowires and account for their beam-induced mechanical behaviour. These results show that direct patterning of one-dimensional conducting nanowires in two-dimensional semiconducting materials with nanometre precision is possible using electron-beam-based techniques.

We report first-principles total-energy electronic-structure calculations in the density-functional theory performed for hexagonally bonded honeycomb sheets consisting of B, N, and C atoms. We find that the ground state of BNC sheets with particular stoichiometry is ferromagnetic. Detailed analyses of energy bands and spin densities unequivocally reveal the nature of the ferromagnetic ordering, leading to an argument that the BNC sheet is a manifestation of the flat-band ferromagnetism.