Since the discovery of the first drum-like CoB16- complex, metal-doped drum-like boron nanotubular structures have been investigated with various metal dopants and different tubular size, forming a new class of novel ...Since the discovery of the first drum-like CoB16- complex, metal-doped drum-like boron nanotubular structures have been investigated with various metal dopants and different tubular size, forming a new class of novel nanostructures. The CoB16- cluster was found to be composed of a central Co atom coordinated by two fused B8 rings in a tubular structure, representing the potential embryo of metal-filled boron nanotubes and providing opportunities to design one-dimensional metal-boron nanostructures. Here we report improved photoelectron spectroscopy and a more in-depth electronic structure analysis of CoB16-, providing further insight into the chemical bonding and stability of the drum-like doped boron tubular structures. Most interestingly, we find that the central Co atom has an unusually low oxidation state of ?1 and neutral CoB16 can be viewed as a charge transfer complex (Co-@BB16+), suggesting both covalent and electrostatic interactions between the dopant and the boron drum.展开更多
Nanotwinned cubic boron nitride(nt-cBN) with remarkable hardness, toughness, and stability has attracted widespread attention due to its distinct scientific and industrial importance. The key for nt-cBN synthesis is t...Nanotwinned cubic boron nitride(nt-cBN) with remarkable hardness, toughness, and stability has attracted widespread attention due to its distinct scientific and industrial importance. The key for nt-cBN synthesis is to adopt an onion-like BN(oBN) nano-precursor and induce phase transition under high pressure. Here, we found that the size change of oBN used greatly affected the mechanical performance of products. With the precursor size decreasing from^320 to 90 nm, the Vickers hardness of nanostructured products improved from 61 to 108 GPa, due to the fact that large oBN nanoparticles possessed more flattened, orderly and graphite-like shell layers, in sharp contrast to the highly wrinkled and imperfect layers in small-diameter nanoparticles, thus resulting in the apparent reduction of ultrafinetwin substructure in the synthetic products. This study reveals that only small oBN precursor could produce complete ultrafine nt-cBN with outstanding performance. A practical route was proposed to further improve the performance of this important material.展开更多
Binderless nanotwinned cubic boron nitride(nt-cBN) synthesized from onion-structured BN precursors under high pressure and high temperature shows a very fine microstructure consisting of densely lamellar nanotwins(ave...Binderless nanotwinned cubic boron nitride(nt-cBN) synthesized from onion-structured BN precursors under high pressure and high temperature shows a very fine microstructure consisting of densely lamellar nanotwins(average thickness of 4 nm) within nanograins. The unique nanotwinned microstructure offers high hardness, wear resistance, fracture toughness, and thermal stability which are essential for advanced cBN tool materials. Thus, a circular micro tool of nt-cBN was fabricated using femtosecond laser contour machining followed by focused ion beam precision milling. Thereafter turning tests were performed on hardened steel using the studied micro tool. To evaluate the cutting performance, the machined surface quality and subsurface damage of the hardened steel were characterized. The wear mechanism of the nt-cBN micro tool was also investigated. It is found that the fabricated nt-cBN micro tool can generate high quality surface with surface roughness less than 7 nm and nanograin subsurface of about 500 nm deep. In addition, abrasive wear is found to be the dominant wear mechanism of the nt-cBN micro tool in turning hardened steel. These results indicate that nt-cBN has outstanding potential for ultra-precision cutting hardened steel.展开更多
We present a system study on the electronic structure and optical property of boron doped semiconducting graphene nanoribbons using the density functional theory. Energy band structure, density of states, deformation ...We present a system study on the electronic structure and optical property of boron doped semiconducting graphene nanoribbons using the density functional theory. Energy band structure, density of states, deformation density, Mulliken popular and optical spectra are considered to show the special electronic structure of boron doped semiconducting graphene nanoribbons. The C-B bond form is discussed in detail. From our analysis it is concluded that the Fermi energy of boron doped semiconducting graphene nanoribbons gets lower than that of intrinsic semiconducting graphene nanoribbons. Our results also show that the boron doped semiconducting graphene nanoribbons behave as p-type semiconducting and that the absorption coefficient of boron doped armchair graphene nanoribbons is generally enhanced between 2.0 eV and 3.3 eV. Therefore, our results have a great significance in developing nano-material for fabricating the nano-photovoltaic devices.展开更多
In this article, a detailed investigation of the cross-section structure of a fivefold twinned boron carbide nanorod is presented. TEM observations reveal that the nanorod possesses a remarkable pseudo-fivefold twinne...In this article, a detailed investigation of the cross-section structure of a fivefold twinned boron carbide nanorod is presented. TEM observations reveal that the nanorod possesses a remarkable pseudo-fivefold twinned cross-section which consists of eight subcrystals packing around its fivefold axis. It is proposed that the negative angular mismatch of 5° for the unrelaxed boron carbide nanowires, which arises from the imperfectness of filling five twinned segments into a 360° solid space, is to be accommodated in one single subunit. The nanorod is found to be free from damage during sample preparation and it retains the intrinsic structural distortions of boron carbide nanowires.展开更多
基金supported by the National Natural Science Foundation of China (No.21590792, No.91426302, and No.21433005)supported by the U.S. National Science Foundation (CHE-1763380)
文摘Since the discovery of the first drum-like CoB16- complex, metal-doped drum-like boron nanotubular structures have been investigated with various metal dopants and different tubular size, forming a new class of novel nanostructures. The CoB16- cluster was found to be composed of a central Co atom coordinated by two fused B8 rings in a tubular structure, representing the potential embryo of metal-filled boron nanotubes and providing opportunities to design one-dimensional metal-boron nanostructures. Here we report improved photoelectron spectroscopy and a more in-depth electronic structure analysis of CoB16-, providing further insight into the chemical bonding and stability of the drum-like doped boron tubular structures. Most interestingly, we find that the central Co atom has an unusually low oxidation state of ?1 and neutral CoB16 can be viewed as a charge transfer complex (Co-@BB16+), suggesting both covalent and electrostatic interactions between the dopant and the boron drum.
基金the financial support of the National Natural Science Foundation of China(51472213,51332005,51572235,51722209 and 51525205)the National Key R&D Program of China+3 种基金the 100 Talents Plan of Hebei Province(E2016100013)the Natural Science Foundation for Distinguished Young Scholars of Hebei Province of China(E2018203349)the Key R&D Program of Hebei Province of China(17211110D)China Postdoctoral Science Foundation(2017M620097)
文摘Nanotwinned cubic boron nitride(nt-cBN) with remarkable hardness, toughness, and stability has attracted widespread attention due to its distinct scientific and industrial importance. The key for nt-cBN synthesis is to adopt an onion-like BN(oBN) nano-precursor and induce phase transition under high pressure. Here, we found that the size change of oBN used greatly affected the mechanical performance of products. With the precursor size decreasing from^320 to 90 nm, the Vickers hardness of nanostructured products improved from 61 to 108 GPa, due to the fact that large oBN nanoparticles possessed more flattened, orderly and graphite-like shell layers, in sharp contrast to the highly wrinkled and imperfect layers in small-diameter nanoparticles, thus resulting in the apparent reduction of ultrafinetwin substructure in the synthetic products. This study reveals that only small oBN precursor could produce complete ultrafine nt-cBN with outstanding performance. A practical route was proposed to further improve the performance of this important material.
基金supported by the National Natural Science Foundation of China(Grant Nos.51205343,51332005&51421091)Hebei Provincial Science Foundation of China(Grant No.E2016203372)
文摘Binderless nanotwinned cubic boron nitride(nt-cBN) synthesized from onion-structured BN precursors under high pressure and high temperature shows a very fine microstructure consisting of densely lamellar nanotwins(average thickness of 4 nm) within nanograins. The unique nanotwinned microstructure offers high hardness, wear resistance, fracture toughness, and thermal stability which are essential for advanced cBN tool materials. Thus, a circular micro tool of nt-cBN was fabricated using femtosecond laser contour machining followed by focused ion beam precision milling. Thereafter turning tests were performed on hardened steel using the studied micro tool. To evaluate the cutting performance, the machined surface quality and subsurface damage of the hardened steel were characterized. The wear mechanism of the nt-cBN micro tool was also investigated. It is found that the fabricated nt-cBN micro tool can generate high quality surface with surface roughness less than 7 nm and nanograin subsurface of about 500 nm deep. In addition, abrasive wear is found to be the dominant wear mechanism of the nt-cBN micro tool in turning hardened steel. These results indicate that nt-cBN has outstanding potential for ultra-precision cutting hardened steel.
基金supported by the Natural Science Foundation of Fujian Province of China (Grant No. A0220001)Science Research Project of Leshan Vocational & Technical College (Grant No. KY2011001)the Key Research Project in Science and Technology of Leshan (Grant No. 2011GZD050)
文摘We present a system study on the electronic structure and optical property of boron doped semiconducting graphene nanoribbons using the density functional theory. Energy band structure, density of states, deformation density, Mulliken popular and optical spectra are considered to show the special electronic structure of boron doped semiconducting graphene nanoribbons. The C-B bond form is discussed in detail. From our analysis it is concluded that the Fermi energy of boron doped semiconducting graphene nanoribbons gets lower than that of intrinsic semiconducting graphene nanoribbons. Our results also show that the boron doped semiconducting graphene nanoribbons behave as p-type semiconducting and that the absorption coefficient of boron doped armchair graphene nanoribbons is generally enhanced between 2.0 eV and 3.3 eV. Therefore, our results have a great significance in developing nano-material for fabricating the nano-photovoltaic devices.
基金supported by the National Basic Research Program of China ("973" Project) (Grant No. 2009CB623701)the National Nature Science Foundation of China (Grant No. 50831160521)
文摘In this article, a detailed investigation of the cross-section structure of a fivefold twinned boron carbide nanorod is presented. TEM observations reveal that the nanorod possesses a remarkable pseudo-fivefold twinned cross-section which consists of eight subcrystals packing around its fivefold axis. It is proposed that the negative angular mismatch of 5° for the unrelaxed boron carbide nanowires, which arises from the imperfectness of filling five twinned segments into a 360° solid space, is to be accommodated in one single subunit. The nanorod is found to be free from damage during sample preparation and it retains the intrinsic structural distortions of boron carbide nanowires.
