GPa. Moreover, there is also a large kinetic barrier for diamond-graphite changes, in either direction. Even downhill spontaneous transformation from diamond to thermodynamically favored graphite (δg ≈ 20 meV/atom lower) is inhibited by a large barrier and would take geological times; good cause for a saying "diamonds are forever." [4] Nevertheless, at the nanoscale, such diamond graphitization [5,6] does occur through the outer atomic layers. This process can be suppressed by saturation of dangling sp 3 surface bonds with adatoms or covalent functional groups, for example, by hydrogenation, which "seals" the carbon in its energetically upper state, diamond. One could speculate that, conversely to graphitization, functionalizing the graphite surface can transform it to sp 3 state of diamond, to some depth; this however, is hindered by the energy taxing sp 3-sp 2 interface, created underneath. Moreover, although the 2D-surface can affect many properties of 3D bulk material, obviously the surface state (reconstruction or chemical passivation) cannot change the thermodynamics of phase preference across the entire macroscopic volume. High pressure, assisted by temperature, remains a prerequisite for getting 3D-diamonds from graphite. With the advent of 2D materials and particularly graphene (Gr), including its bilayer (BLG [7]) and few-layer (FLG [8]) varieties, this paradigm may change. In contrast to 3D bulk, if the sample is of very small, nanometer scale thickness, then its surface chemistry can switch the lattice organization (phase state) throughout. To appreciate the ease of such "phase conversion" by chemistry, one recalls best studied monolayer graphene hydrogenated on both sides into CH composition. It was theoretically proposed [9] and christened "graphane" in its detailed study. [10] Basic notable features distinguishing graphane are the sp 3-hybridizaton of all C-atoms (instead of sp 2 in graphene) and its wide band gap (5.4 eV in the graphane chair conformation, [11] instead of zero in semimetal graphene), which justify considering it as the ultimate, thinnest diamond slab [12] (especially since the bulk diamond surface is also typically H-passivated). The contrast in electronics of graphene and graphane invites possibilities of direct chemical patterning of functional circuitry. [13,14] The choice of active atoms is not limited to H, but can also be fluorine (interesting due to high chemical activity in its attachment to the graphene [13,15]), or chlorine. [16] The kinetics of such transformation was first analyzed in the context of hydrogen storage [17] and spillover [18] media, showing Nearly 2D diamond, or diamane, is coveted as an ultrathin sp 3-carbon film with unique mechanics and electro-optics. The very thinness (≈h) makes it possible for the surface chemistry, for example, adsorbed atoms, to shift the bulk phase thermodynamics in favor of diamond, from multilayer graphene. Thermodynamic theory coupled with atomistic first principles computations predicts not only the reduction of required pres...

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The morphology and electronic properties of single and few-layer graphene films nanostructured by the impact of heavy high-energy ions have been studied. It is found that ion irradiation leads to the formation of nano-sized pores, or antidots, with sizes ranging from 20 to 60 nm, in the upper one or two layers. The sizes of the pores proved to be roughly independent of the energy of the ions, whereas the areal density of the pores increased with the ion dose. With increasing ion energy (>70 MeV), a profound reduction in the concentration of structural defects (by a factor of 2-5), relatively high mobility values of charge carriers (700-1200 cm2 V-1 s-1) and a transport band gap of about 50 meV were observed in the nanostructured films. The experimental data were rationalized through atomistic simulations of ion impact onto few-layer graphene structures with a thickness matching the experimental samples. We showed that even a single Xe atom with energy in the experimental range produces a considerable amount of damage in the graphene lattice, whereas high dose ion irradiation allows one to propose a high probability of consecutive impacts of several ions onto an area already amorphized by the previous ions, which increases the average radius of the pore to match the experimental results. We also found that the formation of "welded" sheets due to interlayer covalent bonds at the edges and, hence, defect-free antidot arrays is likely at high ion energies (above 70 MeV).

Phase diagrams of carbon, and those focusing on the graphite-to-diamond transitional conditions in particular, are of great interest for fundamental and applied research. The present study introduces a number of experiments carried out to convert graphite under high-pressure conditions, showing a formation of stable phase of fullerene-type onions cross-linked by sp-bonds in the 55-115 GPa pressure range instead of diamonds formation (even at temperature 2000-3000 K) and the already formed diamonds turn into carbon onions. Our results refute the widespread idea that diamonds can form at any pressure from 2.2 to 1000 GPa. The phase diagram built within this study allows us not only to explain the existing numerous experimental data on the formation of diamond from graphite, but also to make assumptions about the conditions of its growth in Earth's crust.

Abstract:In this study, we present a number of experiments on the transformation of graphite, diamond, and multiwalled carbon nanotubes under high pressure conditions. The analysis of our results testifies to the instability of diamond in the 55-115 GPa pressure range, at which onion-like structures are formed. The formation of interlayer sp 3 -bonds in carbon nanostructures with a decrease in their volume has been studied theoretically. It has been found that depending on the structure, the bonds between the layers can be preserved or broken during unloading.

Straining to make a transistor The use of carbon nanotubes (CNTs) as short-channel-length transistors will require control of their chirality, which determines whether they are semiconducting or metallic and if they form strong, low-resistance contacts. Tang et al . fabricated CNT intramolecular transistors by progressive heating and straining of individual CNTs within a transmission electron microscope. Changes to chirality along sections of the nanotube created metallic-to-semiconducting transitions. A semiconducting nanotube channel was covalently bonded to the metallic nanotube source and drain regions. The resulting CNT intramolecular transistors had channel lengths as short as 2.8 nanometers. —PDS

In a topological semimetal with Dirac or Weyl points, the bulk-boundary correspondence principle predicts a gapless edge mode if the essential symmetry is still preserved at the surface. The detection of such topological surface state has been considered as the fingerprint prove for crystals with nontrivial topological bulk band. On the contrary, it has been proposed that even with symmetry broken at the surface, a new surface band can emerge in nonsymmorphic topological semimetals. The symmetry reduction at the surface lifts the bulk band degeneracies and produces an unusual "floating" surface band with trivial topology. Here, we first report quantum transport probing to ZrSiSe thin flakes and directly reveal transport signatures of this new surface state. Remarkably, though topologically trivial, such a surface band exhibits substantial two-dimensional Shubnikov−de Haas quantum oscillations with high mobility, which signifies a new protection mechanism and may open applications for quantum computing and spintronic devices.

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