Boron nitride (BN) structures are featured by their excellent thermal and chemical stability and unique electronic and optical properties. However, the lack of controlled synthesis of quality samples and the electrically insulating property largely prevent realizing the full potential of BN nanostructures. A comprehensive overview of the current status of the synthesis of two-dimensional hexagonal BN sheets, three dimensional porous hexagonal BN materials and BN-involved heterostructures is provided, highlighting the advantages of different synthetic methods. In addition, structural characterization, functionalizations and prospective applications of hexagonal BN sheets are intensively discussed. One-dimensional BN nanoribbons and nanotubes are then discussed in terms of structure, fabrication and functionality. In particular, the existing routes in pursuit of tunable electronic and magnetic properties in various BN structures are surveyed, calling upon synergetic experimental and theoretical efforts to address the challenges for pioneering the applications of BN into functional devices. Finally, the progress in BN superstructures and novel B/N nanostructures is also briefly introduced.

(1 of 22)allotropes of boron have been discovered up to now. Four of them are thermodynamically stable, including α-rhombohedral, [6] β-rhombohedral, [7] γ-orthorhombic, [1f,2d,8] and β-tetragonal boron crystals. [1d,9] These materials are often called boron-icosahedral cluster solids (B-ICSs), [5b,10] consisting of icosahedral closo-cluster B 12 to link with each other or with other clusters to form boron allotropes and B-rich compounds, such as various types of BN, [11] B 12 As 2 , [12] B 12 P 2 , [13] B 12 O 2 , [14] YB 66 , [15] AlB 12 , [16] and boron carbide. [17] Apart from three-dimensional (3D) boron icosahedral solids, 2D boron also exhibits many unique structures owning to its electron deficiency, different from other well-known 2D materials. Generally, 2D boron crystals can be classified into three categories: 1) graphene-like atomically monolayered boron sheets, [18] 2) 2D boron structures with thickness of a single or a few unit cells, [19] and 3) new kinds of 2D boron structures reported recently. [20] For the first category, "borophene" was coined to refer to a general class of atomically thin boron sheets, [21] unlike other structures with the suffix ene, where each name always corresponds to a certain structure. For example, graphene, as the most attractive 2D crystals, is a single monolayer of carbon atoms, while phosphorene (monolayered black phosphorus) exists with puckered layer structures in nature. Both graphene and phosphorene have corresponding bulk counterparts, allowing for facile access to 2D-layered van der Waals structures through mechanical exfoliations. Other elemental 2D materials, such as silicene, [22] germanene, [23] stanene, [24] arsenene, [25] and antimonene, [26] actually do not have layered bulk counterparts. Similarly, 2D single-layered boron could not be produced by exfoliating from its bulk materials because there is no layered bulk boron. As a result, it is suggested that 2D boron sheets can be synthesized via chemical vapor deposition, thermal evaporation deposition, or molecular beam epitaxy. In the past decade, extensive theoretical efforts have been paid to investigate possible boron sheets, many of which have been predicted to have potential applications in electronic devices, [18c,d] photoelectric devices, [27] superconductivity, [20a,28] field-emission (FE) materials, [29] hydrogen storage media, [30] and lithium-ion batteries. [31] However, the fabrication of 2D boron crystals is a great challenge. Until very recently, three types of monolayered Boron, as a unique element nearest to carbon in the periodic table, has been predicted to form many distinctive two-dimensional (2D) structures that significantly differ from other well-studied 2D materials, owning to its exceptional ability to form strong covalent two-center-two-electron bonds as well as stable electron-deficient multi-center-two-electron bonds. Until recently, the successful syntheses of atomically thin crystalline 2D boron sheets (i.e., borophenes) provoked growing passion in 2D boron crysta...

Bi2O2Se is emerging as a photosensitive functional material for optoelectronics, and its photodetection mechanism is mostly considered to be a photoconductive regime in previous reports. Here, the bolometric effect is discovered in Bi2O2Se photodetectors. The coexistence of photoconductive effect and bolometric effect is generally observed in multiwavelength photoresponse measurements and then confirmed with microscale local heating experiments. The unique photoresponse of Bi2O2Se photodetectors may arise from a change of hot electrons during temperature rises instead of photoexcited holes and electrons. Direct proof of the bolometric effect is achieved by real‐time temperature tracking of Bi2O2Se photodetectors under time evolution after light excitation. Moreover, the Bi2O2Se bolometer shows a high temperature coefficient of resistance (−1.6% K−1), high bolometric coefficient (−31 nA K−1), and high bolometric responsivity (>320 A W−1). These findings offer a new approach to develop bolometric photodetectors based on Bi2O2Se layered materials.

Low‐dimensional materials exhibit many exceptional properties and functionalities which can be efficiently tuned by externally applied force or fields. Here we review the current status of research on tuning the electronic and magnetic properties of low‐dimensional carbon, boron nitride, metal‐dichalcogenides, phosphorene nanomaterials by applied engineering strain, external electric field and interaction with substrates, etc, with particular focus on the progress of computational methods and studies. We highlight the similarities and differences of the property modulation among one‐ and two‐dimensional nanomaterials. Recent breakthroughs in experimental demonstration of the tunable functionalities in typical nanostructures are also presented. Finally, prospective and challenges for applying the tunable properties into functional devices are discussed. WIREs Comput Mol Sci 2016, 6:324–350. doi: 10.1002/wcms.1251For further resources related to this article, please visit the WIREs website.Conflict of interest: The authors have declared no conflicts of interest for this article.

No abstract

Synthetic two-dimensional (2D) materials without layered bulk allotropes are approaching a new frontier of materials flatland, one with properties richer than those of graphene-like materials. This is the case even as only a few chemical elements and blends have shown synthetic 2D forms. While hydrogen and metals are earth-abundant and form numerous compounds, rarely are 2D materials with only robust metal−hydrogen bonds. Here, a large new family of 2D materials is found from metal hydrides by high-throughput computational search augmented with first-principles calculations. There are 110 thermally and dynamically stable 2D materials that range from metallic materials to wide-gap semiconductors. A subgroup of these materials even varies from topological insulators to nodal-loop semimetals as well as from antiferromagnetic semiconductors to ferromagnetic halfmetals. Unexpectedly, these monolayers resemble graphene in an ability to form weak interlayer interaction due to the variable multicenter bonding of hydrogen that eliminates the otherwise prevalent dangling bonds, rather than the covalent bonds between stacked layers as in previously reported synthetic 2D materials. This feature will favor potential experimental synthesis of these metal hydride monolayers.

The photo-electrical properties of trilayer MoSe 2 nano°akes, fabricated by mechanical exfoliation, were systematically studied in this paper. The trilayer MoSe 2 nano°akes are n-type and possess a high gate modulation (On/O® ratio is larger than 10 5 Þ and a relatively high carrier mobility (1.79 cm 2 V À1 s À1 Þ. The¯eld e®ect transistor (FET) device of MoSe 2 shows sensitive photo response, high photoresponsivity (R ¼ 26:2 mA/W), quick response time (t < 20 ms), high external quantum e±ciency ( ¼ 5:1%Þ and high detection rate (D ¼ 2:7 Â 10 9 W À1 Þ for red and near-infrared wavelength. These results showed that the device based on few-layer MoSe 2 nano°akes exhibited good photo-electrical properties, which might open a new way to develop few-layer MoSe 2 -based material in the application of FETs and optoelectronics.

Our density functional theory calculations show that the energy gap of bilayer α-graphyne can be modulated by a vertically applied electric field and interlayer strain. Like bilayer graphene, the bilayer α-graphyne has electronic properties that are hardly changed under purely mechanical strain, while an external electric field can open the gap up to 120 meV. It is of special interest that compressive strain can further enlarge the field induced gap up to 160 meV, while tensile strain reduces the gap. We attribute the gap variation to the novel interlayer charge redistribution between bilayer α-graphynes. These findings shed light on the modulation of Dirac cone structures and potential applications of graphyne in mechanical-electric devices.