论文2015阅读次数 [1449] 发布时间 :2015-04-01 17:18:24
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13.From ice superlubricity to quantum friction: Electronic repulsivity and phononic elasticity
Friction 3(2015)，294-319
Xi Zhang*, Yongli Huang, Zengsheng Ma, Lengyuan Niu, Chang Qing Sun*
Superlubricity means non-sticky and frictionless when two bodies are set contacting motion. Although this occurrence
has been extensively investigated since 1859 when Faraday firstly proposed a quasiliquid skin on ice, the mechanism behind the superlubricity remains uncertain. This report features a consistent understanding of the superlubricity pertaining to the slipperiness of ice, self-lubrication of dry solids, and aqueous lubricancy from the perspective of skin bond-electron-phonon adaptive relaxation. The presence of nonbonding electron polarization, atomic or molecular undercoordination, and solute ionic electrification of the hydrogen bond as an addition, ensures the superlubricity. Nonbond vibration creates soft phonons of high magnitude and low frequency with extraordinary adaptivity and recoverability of deformation. Molecular undercoordination shortens the covalent bond with local charge densification, which in turn polarizes the nonbonding electrons making them localized dipoles. The locally pinned dipoles provide force opposing contact, mimicking magnetic levitation and hovercraft. O:H−O bond electrification by aqueous ions has the same effect of molecular undercoordination but it is throughout the entire body of the lubricant. Such a Coulomb repulsivity due to the negatively charged skins and elastic adaptivity due to soft nonbonding phonons of one of the contacting objects not only lowers the effective contacting force but also prevents charge from being transited between the counterparts of the contact. Consistency between theory predictions and observations evidences the validity of the proposal of interface elastic Coulomb repulsion that serves as the rule for the superlubricity of ice, wet and dry frictions, which also reconciles the superhydrophobicity, superlubricity, and supersolidity at contacts.
12. Tensile strain-induced magnetism transition in multilayer graphene with excess electrons: Stability of the edge-quantum well
AIP ADVANCES 5(2015), 127106 (PDF-File)
Lei Yang and Dongfeng Diao
The stability of edge-quantum well-induced strong magnetism of multilayer armchair graphene nanoribbon (AGNR) with excesselectrons was investigated under applied tensile strain by density functional theory (DFT) calculations. The results indicated that: (1) The strain along the armchair edge direction led to a transition of the multilayer AGNRs from ferromagnetic state to nonmagnetic state when the strain increased to a critical value; (2) The strain induced bond length changes reduced the stability of the edge-quantum well in terms of the reduction of the electrons capturing capacity; and (3) The spin splitting of the energy bands near the Fermi level reduced with the increase of the strain, resulting in the decrease of the spin moment. This finding suggests that the magnetic properties of graphene have strong dependence on its strain states, which is crucial to the design of graphene-based magnetic devices.
Applied Surface Science 362 (2016) 49–55(PDF-File)
Xue Fan, Dongfeng Diao∗
We report a nanoscale adhesion induced nano-response
in terms of re-indentation during in situ trans-mission electronmicroscope (TEM) nanoindentation on the carbon coating with silicon substrate. Theadhesive force generated with nanoindentation was measured, and re-indentation phenomenon duringunloading with displacement sudden drop and external loading force change from tension to com-pression was found. The occurrence of re-indentation during unloading was ascribed to the adhesiveforce of the contact interface between the indenter and the coating surface. Adhesion energies releasedfor re-indentation processes were quantitatively analyzed from the re-indentation load–displacementcurves, and carbon coating reduced the impact of adhesion for silicon substrate. The adhesion inducednano-response of contact surfaces would affect the reliability and performance of nano devices.
10. Restructured graphene sheets embedded carbon film by oxygen plasma etching and its tribological properties
Applied Surface Science 357 (2015) 771–776（PDF-File）
Meiling Guo, Dongfeng Diao*, Lei Yang, Xue Fan
An oxygen plasma etching technique was introduced for improving the tribological properties of thegraphene sheets embedded
carbon (GSEC) film in electron cyclotron resonance plasma processing system. The nanostructural changing in the film caused by oxygen plasma etching was examined by transmission electron microscope, Raman spectroscopy and X-ray photoelectron spectroscopy, showing that the 3 nm thick top surface layer was restructured with smaller graphene nanocrystallite size as well as higher sp3bond fraction. The surface roughness, mechanical behavior and tribological properties of the original GSECand oxygen plasma treated GSEC films were compared. The results indicated that after the oxygen plasma treatment, the average roughness decreased from 20.8 ± 1.1 nm to 1.9 ± 0.1 nm, the hardness increased from 2.3 ± 0.1 GPa to 2.9 ± 0.1 GPa, the nanoscratch depth decreased from 64.5 ± 5.4 nm to 9.9 ± 0.9 nm,and the wear life increased from 930 ± 390 cycles to more than 15,000 frictional cycles. The origin of the improved tribological behavior was ascribed to the 3 nm thick graphene nanocrystallite film. This finding can be expected for wide applications in nanoscale surface engineering.
9. Stable and super-low friction of amorphous carbon nitride coatings in nitrogen gas by using two-step ball-on-disk friction test
Lubrication Science 27(2015), 137–149(PDF-File)
Pengfei Wang*, Masakatsu Sugo and Koshi Adachi
Effect of running-in process on friction behaviour of carbon nitride (CNx) coating in N2 gas stream was investigated
with a newly introduced two-step ball-on-disk friction test, where the rubbed Si3N4 ball in the pre-sliding (step 1) was replaced by a new CNx-coated Si3N4 ball in the subsequent sliding stage under N2 gas (step 2). The two-step friction test is clarified to be a simple but effective technique for obtaining contact material combination of self-mated CNx coatings and for achieving stable and low frictions of CNx coatings. Friction coefficients of CNx/CNx in N2 gas stream decrease greatly from 0.07 without pre-sliding to less than 0.025 in two-step friction tests. The minimum friction coefficient of 0.004 was obtained by introducing 500 cycles of pre-sliding in ambient air. These stable and low frictions are attributed to the generation of self-mated CNx coatings and the formation of a lubricious layer on the disk surface.
8. Three-layered sandwich structured carbon film prepared by sputtering and ion/electron/ion alternative irradiation
Surface & Coatings Technology 278 (2015), 12-17(PDF-File)
Wenlei Zhang, Dongfeng Diao*, Xue Fan
The electron irradiated carbon film based on electron cyclotron resonance (ECR) sputtering technology has been proved to
have both high conductivity and paramagnetism. However, the relatively low hardness, wear life and high surface roughness value limit its application in Micro-electromechanical Systems (MEMS). To improve these properties, the sandwich structured carbon films with different modulation ratios were introduced on silicon (100) wafers by alternative irradiation (ion/electron/ion) technique in ECR sputtering system. The three-layered anostructure of films was measured with a transmission electron microscopy (TEM). The surface roughness of the film can be controlled to 0.19 nm according to the measurement of atomic force microscope (AFM). The unique characteristics of electron irradiated layer remained stable after irradiation through the analyzing of Raman spectroscopy. The mechanical properties (including hardness, elastic modulus, fracture behavior) and wear life were improved significantly due to the sandwich structure. The results showed that the sandwich structured carbon film is a kind of functional material equipped with enhanced mechanical and tribological properties.
7. Coordination-Resolved Electron Spectrometrics.
Chemical reviews 115(2015), 6746-6810
Xinjuan Liu#, Xi Zhang#, Maolin Bo#, Lei Li#, Hongwei Tian#, Yanguang Nie#, Yi Sun#, Shiqing Xu*, Yan Wang*, Weitao Zheng*, Chang Q.Sun*.
PDF-File：http://pubs.acs.org/doi/abs/10.1021/cr500651m
This treatise reports recent progress in resolving the atomistic, coordination-resolved, dynamic, local, and quantitative information on bond relaxation in length and energy, charge quantum entrapment and polarization, energy density, and atomic cohesive energy pertaining to the under- and heterocoordinated atoms and their joint effect. Atomic undercoordination refers to atoms associated with grain boundaries, homogeneous adatoms, point defects, solid or liquid skins, terrace edges, and nanostructures of various shapes and dimensionalities. Atomic heterocoordination means those associated with alloys, compounds, chemisorbed skins, dopants, impurities, and interfaces.
6.Potential Paths for the Hydrogen-Bond Relaxing with (H2O)(N) Cluster Size
Journal of Physical Chemistry C 119(2015), 16962-16971 （PDF-File）
Yongli Huang#, Xi Zhang#, Zengsheng Ma, Guanghui Zhou, Yinyan Gong, Chang Q.Sun*.
Relaxation of the hydrogen bond (O:H−O) between oxygen ions of undercoordinated molecules fascinates the behavior of water nanodroplets and nanobubbles. However, probing such potentials remains yet far from reality.
Here we show that the Lagrangian solution (Huang et al. J. Phys. Chem. B 2013, 117, 13639) transforms the observed H−O bond (x = H) and O:H nonbond (x = L) lengths and their characteristic phonon frequencies (dx, ωx) (Sun et al. J. Phys. Chem. Lett. 2013, 4, 2565) into their respective force constants and cohesive energies (kx, Ex), which results in mapping of the potential paths for the O:H−O bond relaxing with (H2O)N cluster size. Results show that molecular undercoordination not only reduces its size (H−O length dH) with enhanced H−O energy from the bulk value of 3.97 to 5.10 eV for a H2O monomer but also enlarges their separation (O:H distance dL) with O:H energy reduction from 95 to 35 meV for a dimer. The H−O energy gain raises the melting point of water skin from the bulk value 273 to 310 K, and the O:H energy loss lowers the freezing temperature of a 1.4 nm sized droplet from the bulk value 258 to 202 K, which indicates droplet size induced dispersion of the quasisolid phase boundaries.
5. A nanoscale temperature-dependent heterogeneous nucleation theory
Journal of Applied Physics 117(2015), 224303 (PDF-File)
Y. Y. Cao and G. W. Yang*
Classical nucleation theory relies on the hypothetical equilibrium of the whole nucleation system, and neglects the thermal
fluctuations of the surface; this is because the high entropic gains of the (thermodynamically extensive) surface would lead to multiple stable states. In fact, at the nanometer scale, the entropic gains of the surface are high enough to destroy the stability of the thermal equilibrium during nucleation, comparing with the whole system. We developed a temperature-dependent nucleation theory to elucidate the heterogeneous nucleation process, by considering the thermal fluctuations based on classical nucleation theory. It was found that the temperature not only affected the phase transformation, but also influenced the surface energy of the nuclei. With changes in the Gibbs free energy barrier, nucleation behaviors, such as the nucleation rate and the critical radius of the nuclei, showed temperature-dependent characteristics that were different from those predicted by classical nucleation theory. The temperature-dependent surface energy density of a nucleus was deduced based on our theoretical model. The agreement between the theoretical and experimental results suggested that the developed nucleation theory has the potential to contribute to the understanding and design of heterogeneous nucleation at the nanoscale.
4. Nanosized graphene crystallite induced strong magnetism in pure carbon films
Nanoscale 7 (2015) 4475-4481 (PDF-File)
Chao Wang, Xi Zhang and Dongfeng Diao*
We report strong magnetism in pure carbon films grown by electron irradiation assisted physical vapor deposition in
electron cyclotron resonance plasma. The development of graphene nanocrystallites in the amorphous film matrix, and the dependence of the magnetic behavior on amorphous, nanocrystallite and graphite-like structures were investigated. Results were that the amorphous structure shows weak paramagnetism, graphene nanocrystallites lead to strong magnetization, and graphite-like structures corresponded with a lower magnetization. At a room temperature of 300 K, the highest saturation magnetization of 0.37 emu g−1 was found in the nanosized graphene nanocrystallite structure. The origin of strong magnetism in nanocrystallites was ascribed to the spin magnetic moment at the graphene layer edges.
3. Nanoscratching of multi-layer graphene by molecular dynamics simulations
TribologyInternational 88 (2015) 85–88 (PDF-File)
Qi Zhang, DongfengDiao*, MomojiKubo
Graphene or graphene-based materials are becoming a glowing material to be expected to control a frictional behavior at contact interface. However, due to its atomic layer to layer structure, it is difficult to clarify its frictional mechanism through
experimental observation. Therefore, in this paper the frictional behavior of diamond tip nanoscratching on multi-layer graphene was investigated by Molecular Dynamics (MD) simulation. Results show super low frictional behavior of graphene layers when the scratch depth is less than 5.3 Å, when the scratch depth is over this value, the friction coefficient increases at least 10 times which is caused by phase transition of graphene layers. Besides, we discussed the sensitivity of friction coefficient to the shapes of scratch tip and its anisotropy.
2.The Effects of Diamond-Like Carbon Films on Fretting Wear Behavior of Orthodontic Archwire-Bracket Contacts
Journal of Nanoscience and Nanotechnology 15(2015) 4641–4647 (PDF-File)
Ting Kang, Shi-You Huang, Jie-Jie Huang, Qi-Hong Li, Dong-Feng Diao∗, and Yin-Zhong Duan∗
This study aims to assess the effects of diamond-like carbon (DLC) films on fretting wear behavior of orthodontic archwire-
bracket contacts. ‘Mirror-confinement-type electron cyclotron resonance (MCECR) plasma sputtering’ was utilized to deposit carbon films on stainless steel archwires and brackets. Nanostructure of carbon films such as the bonding structure, cross-sectional thickness and surface roughness were studied. The fretting wear behavior of various archwire-bracket contacts were investigated by using a self-developed tester in ambient air and artificial saliva. The results indicated that DLC-coated wires showed significantly low friction coefficient than the uncoated wires independently of the applied environments. Nevertheless, the DLC-coated and uncoated brackets showed no significant differences in the friction coefficient. Microscopic analysis showed that low wear took place for the DLC-coated surfaces. It is proposed that the application of DLC coating on archwires can decrease the orthodontic fretting wear and coefficient of friction. Unfortunately it does not affect the frictional properties for brackets at present. 1.Hydrogen-bond relaxation dynamics: Resolving mysteries of water ice
Coordination Chemistry Reviews, 285 (2015) 109-165
PDF-File http://www.sciencedirect.com/science/article/pii/S0010854514002756
Yongli Huang#, Xi Zhang#, Zengsheng Ma, Yichun Zhou, Weitao Zheng, Ji Zhou, Chang Q. Sun
We present recent progress in understanding the anomalous behavior of water ice under mechanical com-pression, thermal excitation, and molecular undercoordination (with fewer than four nearest neighborsin the bulk) from the perspective of
hydrogen (O:H O) bond cooperative relaxation. We modestly claimthe resolution of upwards of ten best known puzzles. Extending the Ice Rule suggests a tetrahedral blockthat contains two H2O molecules and four O:H O bonds. This block unifies the density-geometry-size-separation of molecules packing in water ice. This extension also clarifies the flexible and polarizableO:H O bond that performs like a pair of asymmetric, coupled, H-bridged oscillators with short-rangeinteractions and memory as well as extreme recoverability. Coulomb repulsion between electron pairson adjacent oxygen atoms and the disparity between the O:H and the H O segmental interactions relaxthe O:H O bond length and energy cooperatively under stimulation. A Lagrangian solution has enabledmapping of the potential paths for the O:H O bond at relaxation. The H O bond relaxation shifts themelting point, O 1s binding energy, and high-frequency phonon frequency whereas the O:H relaxationdominates polarization, viscoelasticity, and the O:H dissociation energy. The developed strategies haveenabled clarification of origins of the following observations: (i) pressure-induced proton centralization,phase transition-temperature depression and ice regelation; (ii) thermally induced four-region oscillationof the mass density and the phonon frequency over the full temperature range; and (iii) molecular-undercoordination-induced supersolidity that is elastic, hydrophobic, thermally stable, with ultra-lowdensity. The supersolid skin is responsible for the slipperiness of ice, the hydrophobicity and toughness ofwater skin, and the bi-phase structure of nanodroplets and nanobubbles. Molecular undercoordinationmediates the O:H and H O bond Debye temperatures and disperses the quasi-solid phase boundary,resulting in freezing point depression and melting point elevation. O:H O bond memory and water-skinsupersolidity ensures a solution to the Mpemba paradox — hot water freezes faster than its cold. Theseunderstandings will pave the way toward unveiling anomalous behavior of H2O interacting with otherspecies such as salts, acids and proteins, and excitation of H2O by other stimuli such as electrical andmagnetic fields.
