论文2016阅读次数 [991] 发布时间 :2016-04-14 15:34:37

9. Hydrogen-bond potential for ice VIII-X phase transition 

Scientific Reports 6(2016), 37161

Xi Zhang, Shun Chen & Jichen Li

Repulsive force between the O-H bonding electrons and the O:H nonbonding pair within hydrogen bond (O-H:O) is an often overlooked interaction which dictates the extraordinary recoverability and sensitivity of water and ice. Here, we present a potential model for this hidden force opposing ice compression of ice VIII-X phase transition based on the density functional theory (DFT) and neutron scattering observations. We consider the H-O bond covalent force, the O:H nonbond dispersion force, and the hidden force to approach equilibrium under compression. Due to the charge polarization within the O:H-O bond, the curvatures of the H-O bond and the O:H nonbond potentials show opposite sign before transition, resulting in the asymmetric relaxation of H-O and O:H (O:H contraction and H-O elongation) and the H+ proton centralization towards phase X. When cross the VIII-X phase boundary, both H-O and O:H contract slightly. The potential model reproduces the VIII-X phase transition as observed in experiment. Development of the potential model may provide a choice for further calculations of water anomalies.

8. Nanobubble Skin Supersolidity 

Langmuir 32(2016) , 11321−11327

Xi Zhang, Xinjuan Liu, Yuan Zhong, Zhaofeng Zhou, Yongli Huang, and Chang Q. Sun*

Water nanobubbles manifest fascinatingly higher mechanical strength, higher thermal stability, and longer lifetime than macroscopic bubbles; thus, they provide an important impact in applications in the biomedical and chemical industries. However, a detailed understanding of the mechanism behind these mysteries of nanobubbles remains a challenge. Consistency between quantum computations and Raman spectrometric measurements confirmed our predictions that a nanobubble skin shares the same supersolidity with molecular clusters, skins of bulk water, and water droplets because of molecular undercoordination (fewer than four nearest molecular neighbors). Molecular undercoordination (coordination number Zcluster < Zsurface < Zbubble < Zbulk = 4) shortens/extends the H−O/O:H bond and stiffens/softens its corresponding stretching phonons, whose frequency shift is proportional to the square root of the cohesive energy and inversely proportional to the segmental length. The strongly polarized O:H−O bond slows the molecular dynamics and increases the viscosity. The freezing temperature is lowered by the softened O:H bond, and the melting temperature is enhanced by the stiffened H−O bond. Therefore, the supersolid skin makes the nanobubbles thermally more stable, less dense, and stiffer and slows the dynamics of their molecular motion.

7. Low energy electron irradiation induced carbon etching: Triggering carbon film reacting with oxygen from SiO2 substrate

Applied Physics Letters 109(2016), 053104

Cheng Chen,Chao Wang, and Dongfeng Diao

We report low-energy (50–200 eV) electron irradiation induced etching of thin carbon films on a SiO2 substrate. The etching mechanism was interpreted that electron irradiation stimulated the dissociation of the carbon film and SiO2, and then triggered the carbon film reacting with oxygen from the SiO2 substrate. A requirement for triggering the etching of the carbon film is that the incident electron penetrates through the whole carbon film, which is related to both irradiation energy and film thickness. This study provides a convenient electron-assisted etching with the precursor substrate, which sheds light on an efficient pathway to the fabrication of nanodevices and nanosurfaces.

6. Top surface modification of carbon film on its structure,morphology and electrical resistivity using electron-ion hybrid irradiation in ECR plasma 

Surface & Coatings Technology 308 (2016) 50–56

ChaoWang, Cheng Chen, Dongfeng Diao

A two-step electron-ion hybrid irradiation process in electron cyclotron resonance (ECR) plasma was proposed as a flexible method to obtain carbon film with low roughness and electrical conductive surface. By the combination of either electron irradiation or ion irradiation during and after film deposition, two modes of hybrid irradiation were realized: In i-e hybrid mode, smooth amorphous carbon film was firstly deposited under ion irradiation, and its electrical resistivity was reduced from 1.4 to 0.12 Ω·cm−1 after 5-min electron irradiation. In e-i hybridmode, conductive graphene nanocrystallited film was firstly deposited, and its surface Ra roughness was decreased from 15.7 to 0.063 nm after 5-min ion irradiation. The top surface structural transition under electron irradiation in the i-emode were demonstrated by transmission electronmicroscopy (TEM), Raman spectra, X-ray photoelectron spectroscopy (XPS) and atomic forcemicroscopy (AFM), and the effective depth of electron irradiation on carbon film surface were discussed. This study provided a practical route to themassive production of ultra-smooth carbon filmswith novel nanostructure and outstanding physical properties for potential applications in nano-machinery and nano-devices. The hybrid irradiationmethod also expanded theway of plasma utilization in the fields of film deposition and surface modification, and will inspire various new films and coatings with improved top surfaces.

4.Low-energy electron irradiation induced top-surfacenanocrystallization of amorphous carbon film

Applied Surface Science 384 (2016) 341–347

Cheng Chen, Xue Fan *, Dongfeng Diao *

We report a low-energy electron irradiation method to nanocrystallize the top-surface of amorphouscarbon film in electron cyclotron resonance plasma system. The nanostructure evolution of the carbonfilm as a function of electron irradiation density and time was examined by transmission electron micro-scope (TEM) and Raman spectroscopy. The results showed that the electron irradiation gave rise to theformation of sp2nanocrystallites in the film top-surface within 4 nm thickness. The formation of sp2nanocrystallite was ascribed to the inelastic electron scattering in the top-surface of carbon film. Thefrictional property of low-energy electron irradiated film was measured by a pin-on-disk tribometer.The sp2nanocrystallized top-surface induced a lower friction coefficient than that of the original pureamorphous film. This method enables a convenient nanocrystallization of amorphous surface.

3. ECR sputtering and electron/ion alternative irradiation for multilayer carbon films fabrication with tunable layer thickness

Surface & Coatings Technology 296 (2016), 26–32

Peidong Xue, Lei Yang*, Dongfeng Diao*

In this work, we proposed a method of electron cyclotron resonance (ECR) sputtering and electron/ion alternative irradiation to formmultilayer carbon filmswith different single layer thicknesses. The soft electron irradiated layers and protective ion irradiated layers were deposited as the component layers. The transmission electron microscopy (TEM) and Raman spectra proved that the graphene sheets structure in electron irradiated layers could be preserved in multilayer carbon films. We found a rule of the dependence of the surface roughness, mechanical and tribological properties of themultilayer films on the single layer thickness. With the decrease of single layer thickness, the surface roughness decreased and the mechanical and tribological properties improved notably. The mechanisms of the long wear life with low friction coefficient were further discussed based on the hardness enhancement and the cracking length limitation. This work indicated that by decreasing the single layer thickness, ECR sputtering and electron/ion alternative irradiation can fabricate films with combined properties of the component materials, which can be expected for broad nanolayered surface science and engineering applications.

2.Cross-Linking-Induced Frictional Behavior of Multilayer Graphene: Origin of Friction

Tribology Letters 62 (2016), 33

Lei Yang, Qi Zhang, Dongfeng Diao*

The tribological properties of graphene have attracted intensive attentions over the past few years. It was found that the frictional behavior of multilayer graphene was dependent on the multilayer thickness. However, the origin for such phenomenon is still under discussion. In this study, the mechanism of the thickness-dependent friction was explored based on molecular dynamics simulations of the scratching process of multilayer graphene. We found that the friction coefficient dropped dramatically as the number of layers increased under the same scratch depth. Further analysis of the graphene structure variation during the scratching process showed that the amount of the crosslinking decreased when the number of layers increased, which accounts for the dependence of the friction coefficient on the thickness. Finally, a novel chanism was proposed that the thickness-dependent friction of multilayer graphene was caused by the formation of crosslinking between graphene layers. This study provides basic understanding of the origin of friction in multilayer graphene.

1. The adhesion behavior of carbon coating studied by re-indentation during in situ TEM nanoindentation

Applied Surface Science 362 (2016) 49–55

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.